EUCALYPT SOWING AND SEEDFALL

Recirculating Aquaculture Workshop

WASTE WASTE MANAGEMENTMANAGEMENT

James M. Ebeling, Ph.D.James M. Ebeling, Ph.D.

Research EngineerResearch EngineerAquaculture Systems Technologies, LLCAquaculture Systems Technologies, LLC

New Orleans, LANew Orleans, LA

As environmental regulations become more stringent, waste management and disposal will become increasingly important in an aquaculture operation. A proper waste management strategy is now considered critical for maintaining the legality, profitability, and sustainability of any aquaculture facility. The U.S. Environmental Protection Agency (US EPA) has recently published criteria for aquacultural waste discharges and treatment. In addition, each states has the ability to set additional requirements on any discharge or waste disposal. This is an ongoing assessment, which could have a major impact on the industry.

Recirculating Aquaculture Workshop 2

Solids Management

Handling wastewater is a major problem in all animal agriculture systems, but there are substantial differences between aquaculture wastewater and manure from hog or dairy systems. The latter are typically in the range of 5 to 15% suspended solids, while fish wastewater can be anywhere from 0.2 to 4.0% suspended solids. Typical suspended solids concentrations from drum filters used in intensive aquaculture operations are around 0.5%. Suspended solids are captured in a variety of ways, but capture techniques primarily rely on straining, settling, or a combination of both. These systems are reasonably effective for removing suspended solids from the culture water, but require periodic flushing of the device to maintain removal efficiency between flushings. Water lost in the flushing process must of course be replaced with clean or new makeup water.

The large flow rates involved in maintaining water quality and removing suspended solids can result in a significant cumulative waste load discharge from fish farms. Consistently meeting strict discharge standards can also be difficult because pipe, channel, and tank cleaning routines can produce fluctuations in discharge flowrates and in the consistencies and concentrations of waste material. The distribution of the nutrients and organic matter between the dissolved, suspended, and settleable fractions affects the choice of method used and the difficulty of effluent treatment.


• Effluent Treatment for:– Total Suspended Solids (TSS)– Settleable Solids– Biochemical oxygen demand (BOD5)– Total Phosphorus (TP)– Nitrogen

• Total Ammonia Nitrogen (TAN)• Nitrate Nitrogen (NO3-N)

– Pathogens

Solids Capture – Quick Review

Removedwithsolids

The filterable or settleable solids contain most of the phosphorus discharged from tanks (50–85%), but relatively little of the total effluent nitrogen, about 15%. Most of the effluent nitrogen released (75–80%) is in the form of dissolved ammonia or nitrate when nitrification is promoted. The variability in the nutrient and organic material fractionation between dissolved and particulate matter is largely dependent on feed formulation and the opportunity for particulate matter to break apart, because the production of smaller particles increases the rate of nutrient and organic matter dissolution. Fecal matter, uneaten feed, and feed fines can be rapidly broken down into much finer and more soluble particles by water turbulence, fish motion, scouring along a tank/pipe bottom, and pumping. It is much more difficult to remove dissolved and fine particulate matter than larger particles. Therefore, culture tank designs and operating strategies that remove solids rapidly and with the least turbulence, mechanical shear, or opportunity for microbiological degradation are important to help the fish farm meet discharge limits.


Solids Capture – Quick Review

• Gravity Separation• Settling Basins

• Quiescent Zones• Off-line Settling Basins• Tube/Plate Settlers

• Swirl Separators

• Physical Filtration• Microscreen Filters (drum, disc, belt)• Granular Media Filters

Solids are captured by two basic methods: gravity separation and physical filtration. Gravity separation can be done in settling basins or swirl separators and physical filtration can be done with microscreen filters or granular media filters.


Solids Waste Characteristics

600500–1,500334284–415Alkalinity

6.05.0–8.06.76.0–7.2pH

400100–80018.36.8–25.6TAN (mg/L)

6,0002,000–30,0002,7601,590–3,870BOD5 (mg/L)

6550–8082.274.6–86.6TVS (% of TS)

5.02.0–8.01.81.4–2.6Total Solids (%)

TypicalRangeMeanRangeParameter

Domestic SludgeAquacultural Sludge

Chen et al. (1998) summarized the waste production characteristics of the concentrated TSS coming from an RAS and compared it to domestic sludge characteristics (see Table 10.1). Compared with typical municipal sludge, aquacultural sludge has a relatively lower solid content and BOD5 concentration. Total ammonia nitrogen (TAN) is fairly low for fresh aquacultural sludge, but can increase drastically if the sludge is left undisturbed for a period of time and mineralization occurs under anaerobic conditions. Aquaculture sludge has a higher nitrogen and phosphorous content than domestic sludge. The average value of total phosphorous (TP) is 1.3% of the dry solid mass, while the typical domestic sludge contains only 0.7%.


Solids Mass Balance

Feed

O2 CO2 Ammonia BOD, TSS, N, P

Focusing on solid waste, the physical properties of different fish manures can be dramatically different. Tilapia manure is distinctly different than, say, trout feces in that tilapia produce a feces that is encapsulated in a mucous membrane resulting in sausage-like strands. The tilapia fecal strands will float to the surface about 30 minutes or so after being defecated due to gas bubbles being formed in the feces within the strand and then later sink again as gas bubbles diffuse through the membrane strands.

Carbohydrate makeup in tilapia feces will also have an impact on the fecal strand density. In general, higher carbohydrate diets and lower fat diets will result in fecal strands that float more readily than the fecal strands produced when the fish consume higher energy diets; the higher carbohydrate levels result in the fish creating a more definitive mucus membrane for the fecal strand. Digestibility also impacts fecal strands, with lower digestibility resulting in more floating fecal strands. Small changes in nutrient composition can have dramatic impacts on water quality. Be extremely cautious in switching feed formulations.


Waste Management Overview

• Treatment processes result in captured solids that must be managed:

• Storage and Thickening• Thickening and Stabilization• Biosolids utilization and disposal• Stabilization of solids for pathogen destruction

The two most common methods used to recycle solid wastes from aquaculture facilities are land application and composting. Most states have guidelines or regulations that govern land application of manure and other organic wastes to fertilize agricultural crops by limiting the land application rates and the amount of associated pathogens, heavy metals, and other contaminants. The land application rates are based on the nutrient content, soil type, and plant nutrient uptake characteristics to prevent runoff or groundwater contamination. Odor problems can also limit land application in developed areas. Finally, the transportation from the point of generation to the application site can be a major factor in the costs of sludge management, since aquaculture sludge, even when thickened, is mostly water.

Before either of these disposal methods can be used, the sludge and effluent wastewater first needs to be transferred to some form of storage system for both sludge thickening and flow equalization. Sludge thickening will reduce the hydraulic loading on subsequent processes. In addition, sludge flow rates and concentrations will vary during cleaning and other maintenance activities. Therefore, some form of flow equalization is needed to equalize the flow on subsequent treatment processes. Sludge storage structures include anaerobic lagoons, earthen ponds, and above and below ground tanks. Sludge thickening can be accomplished by settling basins, lime stabilization, reed beds or wetlands, and sand beds.


Solids Storage and Thickening

Quiescent Zones

Settling Basins

Thickening basins and separate storage structures are both utilized for storing aquacultural sludge. Thickening basins can be designed to accommodate the build-up of solids and provide temporary solids storage capacity. However, as sludge accumulates within these basins they will become less and less effective at solid-liquid separation due to impingement on the proper settling hydraulics, solids flotation due gas bubble production from fermentation, and dissolution of nutrients and organic matter.

In many cases, the thickened sludge from thickening basins is transferred to larger sludge storage structures capable of holding months worth of captured and thickened solids. Sludge storage structures utilized include earthen ponds, above ground tanks, and below ground tanks.



Earthen Ponds

Earthen ponds are generally rectangular basins with inside slopes (horizontal:vertical) of 1.5:1 to 3:1. Depending on site geology and hydrology, earthen ponds can have liners of concrete, geomembrane, or clay. Earthen pond design will include the capacity for storage of precipitation as well as a method for removing solids, Fig. 10.2. In the case where solids will be unloaded via pumping, the solids must be agitated to provide a uniform consistency. Pond agitation may be accomplished with hitch-type propeller agitators that are powered by tractors or by agitation pumps. Propeller agitators work well for large ponds, while chopper-agitator pumps work well for smaller ponds. Solids unloading may also be done with heavy equipment, in which case pond design should include ramp access (maximum slope of 8:1) and suitable load capacity in the unloading work area.



• Slurrystore Tanks

Engineered Storage Products Company

Sludge may also be stored in tank structures, above and below ground. Storage tanks are primarily constructed of reinforced concrete, metal, and wood. Reinforced concrete tanks including both walls, foundation, and floor slab-- may be cast-in-place or they may be constructed of pre-cast wall panels, bolted together, and set on a cast-in-place foundation and floor slab. Metal tanks are also widely used, with the majority being constructed of glass-fused steel panels that are bolted together. There are many manufactured, modular tanks commercially available in reinforced concrete and metal, as well as wood.


Solids Thickening and Stabilization

Captured solids require further dewatering:

3-5%Quiescent Zone Siphon

3-5%Quiescent Zone Siphon

0.01-0.8%Microscreen Filter Backwash

TSS

Captured solids from solids removal processes tend to be dilute, having less than 2% total solids content. These solids may be concentrated or thickened in settling basins up to 5–10% total solids content. Thickening basins operate according to the same discrete particle settling principles previously described. However, because thickening basins receive water with elevated solids content and are concentrating these solids by permitting particle settling, the solids are also subject to compression settling. Compression settling develops when a compressed layer of particles forms at the basin bottom. The particles in this region begin to form a structure of particle-particle contact and the slurry is concentrated further. In general, the overflow rate for sludge thickening basins should be approximately 1.0 m3/m2/hr (3.2 ft3/ft2/hr) with hydraulic retention times of between 20 to 100 minutes.


Solids Thickening

• Solids must be thickened (dewatered) to reduce disposal costs/management.

– Dewatering reduces sludge volume.– Sludge volume for 1,000 lb dry weight solids:

– 12,000 gal 1% TSS – 2,400 gal 5% TSS– 1,200 gal 10% TSS– 800 gal 15% TSS

Solids thickening also significantly reduces disposal cost by reducing volume of sludge.

Thickened sludge in the bottom of thickening basins may be further conditioned by adding lime. Lime addition is an effective method to kill sludge pathogens, reduce odor problems, and improve solids thickening. It is recommended that 15–20 g (0.125–0.167 lbs) of unslaked lime (CaO) per gallon of sludge (10% solids content) be used to achieve a pH of 12 for lime stabilization. In addition to stabilizing the sludge and improving its settling properties, lime stabilization also increases the removal of phosphorus.


Solids Thickening Methods

• Processes to thicken clarifier/filter backwash solids:

• offline settling basins (sludge thickening tanks)• wetlands or sand beds• coagulation/flocculation• belt filters• GeoTextile Bags

Other sludge thickening methods include off line settling basins, wetlands, sand beds, wedgewire sieves, filter presses, centrifuges, vacuum filters, and reed beds.


Off-line Settling Basins

• Designed for solids collection, thickening and storage

• Intermittently loaded from– quiescent zone cleaning– filter backwashing– system cleaning

Off-line settling basins are designed for solids collection, thickening and storage. They have been successfully used for the treatment of slurries from quiescent zone cleaning activities in raceway production, microscreen filter backwash water from recirculation systems and flow from system cleaning activities.


Off-line Settling Tanksat Freshwater Institute


The Freshwater Institute has successfully applied the concept of settling basins to concentrating the backwash coming off of the drum filters. Three off-line settling cones or thickening tanks are used to capture and store solids from the intermittent backwash of three drum filters. The solids-laden backwash flow is introduced intermittently into the top and center of each tank. At the top of each tank, the flow is introduced within a cylinder with an open bottom that is centered within the tank. The cylinder improves the hydraulics of the tank's radial flow by directing the water to first flow down (underneath the cylinder and towards the cone of the tank) and then up as it travels radially towards the effluent collection launder about the top circumference of the tank. These thickening tanks have performed well, capturing 97% of the solids discharged from the microscreen filter backwash flows. In addition, the three settling cones are plumb such that the three waste streams can be directed to a single cone or multiple cones.


Recirculating Aquaculture Systems Short Course


At the top of each tank, the flow is introduced within a cylinder with an open bottom that is centered within the tank. The cylinder improves the hydraulics of the tank's radial flow by directing the water to first flow down (underneath the cylinder and towards the cone of the tank) and then up as it travels radially towards the effluent collection launder about the top circumference of the tank. These thickening tanks have performed well, capturing 97% of the solids discharged from the microscreen filter backwash flows. In addition, the three settling cones are plumb such that the three waste streams can be directed to a single cone or multiple cones.


LARGE structures with solids storage capacity


Big Spring FCS (PA)


Off-line Settling Basins Design

Idaho DEQ (1998) design criteria for off-line settling basins:• overflow rate of 0.0015 ft3/sec flow per ft2 surface area• usually 3.5 ft deep• usually built in pairs• tank MUST capture 85% TSS• TSS effluent CANNOT exceed 100 mg/L in 8 hr composite• settleable solids effluent CANNOT exceed 1.0 ml/L in any

sample

Recommended design criteria by the Idaho Department of Environmental Quality for the trout industry.


Off-line Settling Basin Solids Removal

• OPTION 1: Decant tank, harvest solids with backhoe or front end loader– Let solids dry for several days to 25% to 35% dry weight

• OPTION 2: Sprinkler application to adjacent fields – 0.2% solids dry weight (after mixing solids)

• OPTION 3: Decant tank, then pump out manure– 12% avg. solids dry weight– 20% max. solids dry weight– pumping method influences % solids removed

Some of the options for removing the solids that collect in the settling basins depending upon size and final disposition.


Wetlands – Sand Beds

Created Wetlands drying beds:• combine solids dewatering and disposal• sand drying bed planted with reeds

• plants facilitate dewatering

• loading• 30-60 kg dry solids per year per m2 area• 7-10 cm sludge at 2% solids every 7-21 days• series of beds receive sequential batches

• store solids for 10 years

Depending on the location and local regulations, an aquaculture facility’s only available options for sludge disposal may be limited and costly. However, if transportation costs make sludge disposal on cropland uneconomical, disposing of the sludge on-site within created wetlands may be an attractive alternative. A constructed reed drying bed can provide on-site treatment of a concentrated solids discharge with an uncomplicated, low-maintenance, plant-based system that could reduce solids disposal costs.

Reed drying beds are vertical-flow wetland (VFW) systems that have been used over the past 20 years to treat thickened sludge (1–7% solids) produced in the clarifier underflow at wastewater treatment plants. When used for municipal treatment, these wetlands are loaded with 7 to 10 cm (2.76–3.94 inches) of 2% solids approximately once every 7–21 days (about 30–60 kg/m2/yr. Other much higher hydraulic loading rates are also reported: 25 cm/day, 80 to 240 cm/day and 2,000 to 2,700 cm/day. Clearly, the specific application and the nature of the wastewater will have an impact on any sustained level of infiltration.



CoagulationProcess of decreasing or neutralizing the electric charge on suspended particles

FlocculationProcess of bringing together the microfloc particles to form large agglomerations by the binding action of flocculants

Coagulation/FlocculationCoagulation/Flocculation

Coagulation is the process of decreasing or neutralizing the electric charge on suspended particles or zeta potential. Like electric charges on small particles in water cause them to naturally repel each other and hold the small, colloidal particles apart, keeping them in suspension. The coagulation/flocculation process neutralizes or reduces the negative charge on these particles, which then allows the van der Waals force of attraction to encourage initial aggregation of colloidal and fine suspended materials to form microfloc. Flocculation is the process of bringing together the microfloc particles to form large agglomerations by physically mixing or through the binding action of flocculants, such as long chain polymers.

A classical coagulation/flocculation unit process (Metcalf and Eddy 1991) consists of three separate steps:

Rapid or Flash Mixing: the suitable chemicals (coagulants/ flocculants and if required pH adjusters) are added to the wastewater stream, which is stirred and intensively mixed at high speed.Slow Mixing (coagulation and flocculation): the wastewater is only moderately stirred in order to form large flocs, which are easily settled out. Sedimentation: the floc formed during flocculation is allowed to settle out and is separated from the effluent stream.

Numerous substances have been used as coagulant and flocculation aids, including alum [Al2(SO4)3⋅18H2O], ferric chloride [FeCl3⋅6H2O], ferric sulfate [Fe2(SO4)3], ferrous sulfate [FeSO4⋅7H2O] and lime [Ca(OH)2] (Metcalf and Eddy 1991).



Suspended Solids Removal(Alum, Ferric Chloride, AMD)

Alum in wastewater yields the following reaction:Al2(SO4)3•14 H2O + 3Ca(HCO3)2 ⇔ 3Ca SO4 + 2Al(OH)3 + 6CO2+ 14H2O

Insoluble aluminum hydroxide is a gelatinous floc

Ferric ChlorideFerric Chloride in wastewater yield the following reactionin wastewater yield the following reaction::22FeClFeCl33 ••6H6H22O+ 3Ca(HCOO+ 3Ca(HCO33))22 ⇔⇔ 3CaCl3CaCl22 +2+2Fe(OH)Fe(OH)33 + 6 CO+ 6 CO22 + 12H+ 12H22OO

Insoluble ferric hydroxide is a gelatinous flocInsoluble ferric hydroxide is a gelatinous floc

Aluminum sulfate (alum) is the most commonly used coagulant and is easy to handle and apply and produces less sludge than lime. Its primary disadvantage is that it is most effective over a limited pH range of 6.5 to 7.5. Ferric chloride is also a commonly used coagulant and is effective over a wider pH range of 4 to 11. The ferric hydroxide floc is also heavier than the alum floc, improving its settling characteristics, and reducing the size of the clarifier. Neither ferric sulfate nor ferrous sulfate is commonly used today, but ferric sulfate is slowly replacing ferric chloride because it is easier to store and handle. Lime is commonly used and is effective, but is quite pH dependent and produces a large quantity of sludge requiring disposal.

When alum is added to a wastewater, the following reaction takes place:

Al2(SO4)3 ⋅18 H2O + 3 Ca(HCO3)2 ⇔ 3 CaSO4 + 2 Al(OH)3 + 6 CO2 + 18 H2O (1)

The insoluble aluminum hydroxide, Al(OH)3, is a gelatinous floc that settles slowly through the wastewater, sweeping out the suspended material. Alkalinity is required for the reaction and if not available, must be added at the rate of 0.45 mg/L as CaCO3 for every 1 mg/L alum. Similarly, for ferric chloride:

2 FeCl3 ⋅6 H2O+ 3 Ca(HCO3)2 ⇔ 3 CaCl2 +2 Fe(OH)3 + 6 CO2 + 12 H2O (2)

The insoluble ferric hydroxide, Fe(OH)3, is also a gelatinous floc that settles through the wastewater,sweeping out the suspended material. Alkalinity is required for the reaction and if not available, must be added at the rate of 0.55 mg/L CaCO3 for every 1 mg/L ferric chloride.



Phosphorus Removal(Alum, Ferric Chloride, AMD)

Basic reaction:

Al+3 + HnPO43-n ⇔ AlPO4 + nH+

Fe+3 + HnPO43-n ⇔ FePO4 + nH+

Simplest form of reaction, bench-scale test required to establish actual removal rate

In addition, both aluminum and iron salts can also be used for the chemical precipitation of phosphorus. The basic reactions involved are:

Al+3 + PO4-3 ⇔ AlPO4 (3)

Fe+3 + PO4-

3 ⇔ FePO4(4)

The above equations are the simplest forms of the reaction (Metcalf and Eddy 1991, Lee and Lin 2000). Due to the many other competing reactions, the effects of alkalinity, pH, trace elements, and other compounds in the wastewater, the actual chemical dosage required to remove a given quantity of phosphorus is usually established on the basis of bench-scale test or sometimes pilot-scale tests.



Coagulation/Flocculation Aids(Polymers)

•• charge neutralization (low molecular weight polymers)low molecular weight polymers)

neutralize negative charge on particleneutralize negative charge on particle

•• bridging between particles (high molecular weight high molecular weight

polymers)polymers)

long loops and tail connect particleslong loops and tail connect particles

Polyelectrolytes act in two distinct ways: charge neutralization and bridging between particles. Because wastewater particles are normally charged negatively, low molecular weight cationic polyelectrolytes can act as a coagulant that neutralizes or reduces the negative charge on the particles, similar to the effect of alum or ferric chloride. This has the effect of drastically reducing the repulsive force between colloidal particles, which allows the van der Waals force of attraction to encourage initial aggregation of colloidal and fine suspended materials to form microfloc. The coagulated particles are extremely dense, tend to pack closely, and settle rapidly. If too much polymer is used, however, a charge reversal can occur and the particles will again become dispersed, but with a positive charge rather than negatively charged.

Higher molecular weight polymers are generally used to promote bridging flocculation. The long chain polymers attach at a relatively few sites on the particles, leaving long loops and tails which stretch out into the surrounding water. In order for the bridging flocculants to work, the distance between the particles must be small enough for the loops and tails to connect two particles. The polymer molecule thus attaches itself to another particle forming a bridge. Flocculation is usually more effective the higher the molecular weight of the polymer. If too much polymer is used however, the entire particle surface can become coated with polymer, such that no sites are available to “bridge” with other particles, the ‘hair-ball effect’. In general, high molecular weight polymers produce relatively large, loosely packed flocs, and more fragile flocs (Wakeman and Tarleton, 1999).



Coagulation/Flocculation Aids(Polymers)

High Molecular Weight Long-chain Polymers

• lower dosages requirements• reduced sludge production• easier storage and mixing• MW and charge densities optimized “designer” aids • no pH adjustment required• polymers bridge many smaller particles• improved floc resistance to shear forces

Advantages:

Recently, the use of high molecular weight long-chain polymers has been used as replacement to alum and ferric chloride for flocculation of suspended solids.Advantages of the polymers are:

•lower dosages requirements,•reduced sludge production,•easier storage and mixing,•both the molecular weight and charge densities can be optimized creating “designer” flocculant aids, •no pH adjustment required, •polymers bridge many smaller particles,•improved floc resistance to shear forces.



Evaluation: alum/polymers

98%0.3517.199%109585 mg/LCE 1950

98%0.2713.799%47195 mg/LCE 834

98%0.1611.499%76540.8 mg/LA-120

98%0.5734.898%2015663 mg/LE 38

98%0.261799%108596 mg/LLT 7995

98%0.171099%75570.8 mg/LLT 27

% Removal

Treated sampleRaw sample

% Removal

Treated sample

Raw sample

Reactive Phosphorus (mg/L P)Total Suspended Solids (mg/L)

Optimum DosagePolymer

Based on preliminary tests with alum on the microscreen effluent discharge, a dosage of 60 mg/L was found to yield the best overall removal of TSS and Reactive Phosphorus and thus was used as a guide for all the screening and evaluation tests. The polymers screened were of assorted chemical families, electric charge, molecular weight, and all but three had maximum dosage limits set for potable water by the National Sanitation Foundation. These limits helped determine the dosage range to be tested. The main purpose of the screening was to examine the performance of each alum / polymer combination at several different polymer concentrations, by looking specifically at their ability to remove suspended solids and phosphorus from the treated water. The effectiveness and efficiency of each combination was determined by comparing the initial water quality and the treated water quality. In addition, a control was carried through the Jar Test procedure. At the end of the screening, six polymers and optimal dosage rates were picked for further evaluation. They were selected primarily based on their outstanding performance, but also intentionally selected to have varying chemical composition/structure. For example, three of the polymers chosen exhibited a cationic charge and three an anionic charge. In addition, the degree of electric charge varied from low, medium, high to very high. The same was seen form molecular weights with one very low, two high and two very high. These tests were conducted over a period of several months, insuring a wide variation in the ‘quality’ of the wastewater treated.

The above table summarizes the polymers and the removal efficiencies for TSS and reactive phosphorus. Although a wide range of polymers were used, i.e. chemical families, charge density, molecular weight, results showed excellent removal efficiencies for all of them. Using a combination of alum/polymer, the effluent Total Suspended Solids removal rate was close to 99%, with final TSS values ranging from as low as 4 to 20 mg/L. Reactive phosphorus was reduced by 92 to 99% to as low as 0.16 mg/L-P. Finally, Total Phosphorus was also significantly reduced (98%) with treated effluent concentrations from 0.9 to 3.0 mg/L-P. Polymer dosage requirements were uniform, requiring approximately 3 to 6 mg/L for four of the polymers and less than 1 mg/L for two of the others.



Synergetic Effect of alum/polymers

95.8%45.1%31.0 mg/LMagnafloc E 38

94.4%---0.8No EffectMagnafloc LT 26

94.8%67.8%0.31.0 mg/L†Magnafloc LT 22S

88.1%---0.8No EffectMagnafloc LT 20

96.3%85.1%610 mg/LMagnafloc LT 7995

95.4%91.6%420 mg/LMagnafloc LT 7992

95.3%86.4%820 mg/L†Magnafloc LT 7991

95.2%---8No EffectMagnafloc LT 7990

50 mg/L alum / polymer

polymer50 mg/L alum / polymerpolymerCiba Specialty Chemicals

Percent RemovalTurbidity (NTU) Optimal Dosage

Previous work (Ebeling, et al. 2005a) examined the use of polymers alone to improve settling and RP removal. Table 8 shows the screening performance results from that study combined with screening results from this study for percent removal of turbidity. It is interesting to note, that in several cases, there was no impact of the polymer alone on turbidity, yet there was significant removal of turbidity when used in combination with alum. For example, Magnafloc LT 7991 had little impact alone, but when combined with alum at 50 mg/L dosage, removed 95.2% of the turbidity. In addition, many of the polymers tested alone required substantially greater dosage rates, compared to the combination of alum/polymer.



Other WQ Effects of alum/polymers

218.94.53.60.2190.24CE 1950

207.73.52.70.1910.19CE 834

2917.74.33.60.2220.36A-120

2712.04.73.70.2240.24E 38

218.14.43.70.2160.28LT 7995

3617.84.83.60.2180.32LT 27

719437.73410.80.4300.75Initial Sample

(mg/L)(mg/L)(mg/L N)(mg/L N)(mg/L N)(mg/L N)

CODCBOD5TNNO3-NNO2-NTAN

Although the suspended solids and reactive phosphorus in the discharged effluent was the primary focus of this research, several other parameters were evaluated in a series of separate tests at the optimum polymer dosage. These included pH, alkalinity, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen, total nitrogen, cBOD5, and COD (Table 9). As can be seen from this table, the combination of alum and phosphorus reduced the pH of the treated effluent over the initial sample, from 7.45 to as low as 7.25 to 7.32. This was due to the consumption of alkalinity by the alum reaction, consuming 0.45 mg/L as CaCO3 for every 1.0 mg/L alum dosage. Thus for the 50 mg/L dosage rate of alum, as much as 22.5 g of alkalinity as CaCO3 could be consumed. Although not critical for this particular waste stream, for waste stream with low alkalinity (< 30 mg/L) at this alum dosage rates some form of alkalinity would have to be added to facilitate this chemical reaction. The drop in alkalinity ranged from 1 to 30 mg/L as CaCO3 with an average of 18 mg/L as CaCO3. Although not intended for nitrogen removal, TAN, nitrite-nitrogen, nitrate-nitrogen, and total nitrogen in the effluent were reduced on average by 64%, 50%, 68%, and 87% respectively. Removal rates for both cBOD5 and COD were also significant, with an average value of 97.3% and 96.4%.



Belt Filter

Coagulation/Flocculation TankCoagulation/Flocculation Tank

The Hydrotech belt filter, Model HBF537-1H (Figure 1) was purchased from Water Management Technologies, Inc. (Baton Rouge, LA, http://www.W-M-T.com)). The system consisted of two parts, a mixing/flocculation tank and an inclined belt filter.

The mixing tank was separated into four chambers, three with an approximate volume of 0.28 m3

and one at 0.02 m3. Total volume of the tank was 0.83 m3 (Figure 2). The first and last chambers had variable speed mixing impellers for slow mixing and the smaller, intermediate chamber had a fixed, 10 cm diameter, high speed (1080 rpm) impeller for polymer mixing. As the waste stream enters the first chamber, alum was injected with a variable speed, peristaltic pump (Masterflex pump, Model 7524-40) from a reservoir at a dosing rate of 0, 25, 50 75 and 100 mg alum per Liter of waste stream influent. This was accomplished by mixing a concentrated solution of alum, 2000 g alum in 20 L of spring water and with a waste stream flow rate of 40 Lpm, dosing the waste stream at a rate of 0, 10, 20, 30, and 40 mL/ min of alum solution. The 34 cm diameter impeller mixed the alum at 60 rpm with the wastewater stream and began the coagulation process. The fine particles in the wastewater stream were charge neutralized and began to aggregate into small floc. The wastewater stream then flowed over a weir into the smaller chamber, where polymer was injected at the surface, again using a variable speed peristaltic pump from a reservoir at polymer dosages of 0, 5, 10, 15, 20, and 25 mg polymer per Liter of waste stream influent. The polymer used, Hyperfloc CE 1950 was from Hychem, Inc., Tampa, Fl, USA (http://www.hydchem.com), a high degree of cationic charge, very high molecular weight polyacrylamide. The concentrated polymer was first diluted to approximately 0.2% or 2 g polymer in L of spring water, activated by mixing at high speed, and stored in a polyethylene reservoir. At this concentration, the polymer can be stored for about 24 to 48 hrs. A Masterflex pump, Model 7524-40 was used to accurately meter the required dose. A 1080 rpm, fixed speed impeller than mechanically mixes the polymer into the waste stream with a short, vigorous mixing to maximize dispersion of the polymer and forced the wastewater stream down and into the third chamber. There the polymer began the process of aggregation of the small particles and floc. Finally, the wastewater stream flowed over a weir into the fourth chamber, where a 34 cm diameter impeller at 60 rpm helped flocculate the floc particles into large floc and maintain them in suspension. From here, the waste stream consisting of large floc particles and relatively clear filtrate flowed into the belt filter header box through a 10 cm pipe.



Belt Filter

Belt Filter

The continuous belt of the inclined belt filter was made of polyester cloth with a mesh size of approximately 120 microns and an angled inclination slope of 10 degrees. As the waste stream flowed onto the belt, the filtrate filters through into the lower sump, and as the belt slowly becomes blocked by sludge, the headloss across the belt filter increases until a level sensor activated a motor which starts the endless band moving. The inclined belt filter then gently lifted the floc out of the water and transported it to the end of the belt where it was scraped off of the belt by means of a firm rubber scraper. A wash water jet spray system then cleaned the belt before it rotates back to the inlet end. During the test trials, the wash water was obtained from a separate clean water source, but could be obtained from the filtrate water in the lower sump. The belt wash water was routed back to the head of the microscreen for further processing. As the belt was self cleaning, belt maintenance was kept to a minimum. In this set-up, the clarified, treated wastewater stream flowed into a pump sump and to an aerobic wastewater treatment pond. The concentrated solids sludge were mixed with straw and as needed transported to a composite facility on site. In the event that the belt filter was unable to process all of the influent flow, a by-pass weir diverted the untreated waste stream back to the head of the microscreen filter.



Belt Filter-Sludge

• Alum• 13.2% ± 1.1

• Polymer

• 11.6% ± 2.2

• Alum/Polymer

• 12.6% ± 1.4

Alum:

The average percent solids of the sludge scraped off of the belt by the scrapper bar was 13.2% with a s.d. of 1.1%. This would represent the maximum obtainable from the system, because some of the wash water tends to drain into the solids sump and reduce the overnight composite samples to as low as 5% solids, although this was significantly improved during later test runs. By adding a simple drainage system in the sludge sump, the final percent solids could be substantially improved to 10% solids or higher. Although it needs to be noted, that the final sludge concentration will be to some extent dictated by how the sludge is handled or processed, for example pumped or augured; stored over winter, composted or land applied.

Polymer:The average percent solids of the sludge scraped off of the belt by the scraper bar was 11.6% with a s.d. of 2.2%, slightly less than with alum alone as a coagulation aid. This would represent the maximum obtainable from the system because some of the wash water tends to drain into the solids sump, although this was substantially reduced by a slight equipment modification so that the overnight composite increased to 9.9% solids.

Alum/Polymer:The average percent solids of the sludge scraped off of the belt by the scraper bar was 12.6% with a s.d. of 1.4%, slightly less than with alum or polymer alone as a coagulation aid. This would represent the maximum obtainable from the system because some of the wash water tends to drain into the solids sump, although as previously mentioned this was substantially reduced by a slight equipment modification so that the overnight composite increased to 9.8% solids.



What is a Geotube ®?

• Geotube ® containers are custom fabricated with seaming techniques that resist pressures during pumping operations.

• Geotubes are constructed of Mirafi®high strength woven geotextile

• High flow rate allows liquid to dewater, while containing solids.

One promising new technology for dewatering aquaculture solid waste is the use of geotextile tubes. Geotextile tubes are porous sealed tubular containers constructed of a woven polyethylene material. Geotextile tubes can dewater wastes to over 10% solids in less than a week, and can achieve final solids content over 30%1. Geotextile tubes have successfully been used to dewater animal wastes, municipal wastewater sludges; hazardous wastes, industrial by-products, and dredge spoil. Geotextile tubes are cost effective, site-specific, and mobile, require little maintenance, and can be manufactured for high containment volumes.

Geotextile tubes are porous tubular containers constructed of a woven polyethylene material. Geotextile tubes can dewater wastes to over 10% solids in less than a week, and can achieve a final solids content over 30%. Geotextile tubes have successfully been used to dewater animal wastes, municipal wastewater sludge's, hazardous wastes, industrial by-products, and dredge spoil.



Benefits of Geotube® Technology

• Effective high volume containment.• Efficient dewatering & volume

reduction.• Cost effective.• No special equipment required.• Custom site specific fabrication.• Lower equipment cost.• Low maintenance.• Low labor cost.

Geotextile tubes are cost effective, site-specific, mobile, require little maintenance, and can be manufactured for high containment volumes.



Containment

Containment Dewatering

Disposal

The Geotube ® is pumped with sludge material.As the liquid escapes from the tube, solid particles are trapped inside. The process is repeated until the tube is full.Eventually, the solids can be handled as dry material, increasing options for transportation and disposal



Applications for Aquaculture

Freshwater Applications• Winter Storage of Biosolids• Composting

Marine Applications Tested by Miratech• Marine benthic waste

• Marine fresh cage waste

• Hatchery recirculation and pass through waste

• Processing plant blood water

• Biofouling waste from cleaning shellfish cages

• Biofouling toxic waste (copper) from salmon net cleaning

Geotubes® (Ten Cate Nicolon, Commerce, GA) have successfully been pilot-tested in the aquaculture industry for various marine and inland aquaculture wastes. As part of the waste management system at The Conservation Fund’s Freshwater Institute, there is a need for intermediate-term (2-6 months) storage of solid wastes, and dewatering processes for incorporation into a waste management system. To this end, it was decided to evaluate the efficiency of dewatering aquaculture solid wastes with Geotubes®; concurrent with the evaluation of other advanced dewatering and treatment technologies. Thus a series of standard jar tests were first used to evaluate the effectiveness of several families of polymers for aquaculture waste effluents. A bench-scale Rapid Dewatering Test Unit (RDT) was used to test a number of parameters with small samples of geotextile material, including filtration rates, coagulation/flocculation selection, dewatering time, filtrate quality, and pressure requirements. A series of larger scale tests were then conducted, using a pilot-scale hanging geotextile bag, to further evaluate performance characteristics. Finally, small scale, sealed geotextile bags were pumped full under pressure with polymer injection to simulate normal operating conditions in an intensive aquaculture recirculation system. This paper presents the results of these tests and preliminary evaluation of operating the geotextile bag under pressure.



Research – Large Geobags

• Each of the three bags were operated at a mean hydraulic loading rate of 58.7 Liters/day/m2 geotextile material.

• Solids pumped to the bags for 0.5 minutes each hour (24/7).



Results of Study

47 ± 15309 ± 80517 ± 241cBOD5 (mg/l)

-1587 ±490

28.1 ± 9.91.7 ± 0.6TAN (mg/l)

32 ± 2437.9 ± 1263.8 ± 25Total Nitrogen (mg/l)

-1145 ±574

10.8 ± 3.21.1 ± 0.7Dissolved Reactive P (mg/l)

65 ± 1212.7 ± 4.140.6 ± 16Total Phosphorus (mg/l)

93.0 ± 398 ± 251875 ± 811TSS (mg/l)

% RemovalBag EffluentBag Influent

36 Samples over 3 months


Biosolids Utilization/Disposal

• Composting• Land Application

– Slurry (<1% solids)– Thickened Sludge (>5% solids)

• Contract hauling

There are several options available for final disposal of the solids, including composting and land application.


Composting

Composting is the aerobic biological decomposition of organic matter. It is a natural process that is enhanced and accelerated by the mixing of aquaculture wastes with other ingredients for optimum microbial growth. Composting converts the sludge and other waste products from aquaculture into a stable organic product by converting nitrogen from the unstable ammonia to a more stable organic form. The end result is a product that is safer to use than the original sludge and when applied to land, will improve the soil fertility, tilth, and water holding capacity. In addition, composting reduces the bulk of material that needs to be spread, improves its handling properties, reduces odor, fly and other vector problems and can destroy pathogens.

Composting methods include windrow, static pile, and in-vessel. The windrow method consists of piling the compost mix into long, narrow piles or windrows. To maintain aerobic conditions, this windrow needs to be periodically turned and mixed, exposing the decomposing material to air and to keep the temperatures from getting too high. The static pile method consists of mixing the compost materials and then stacking the mixture on plastic pipe or tubing through which air can be forced or drawn. Small compost piles may not need forced ventilation, if they are highly porous or with a mix that is stacked in layers with highly porous materials. The in-vessel method involves the mixing of the materials in a reactor, building, container, or vessel. Forced ventilation may be required. This process provides a high level of control over moisture, aeration, and temperature.


Composting Bin

Composting of aquaculture wastes requires the mixing in of amendments or bulking agents in the proper proportions to promote aerobic microbial activity and growth and achieve optimum temperatures. This mixture provides a source of energy and nutrients, moisture, and oxygen for the bacteria. The composting amendment is added to the mixture to alter the moisture content, carbon to nitrogen (C:N) ratio, or pH. Many materials are suitable for use as composting amendments, including crop residues, leaves, grass, straw, hay, sawdust, wood chips or shredded paper, and cardboard. The bulking agent is used to improve the ability of the compost to be self-supporting and to increase porosity to allow internal air movement. Wood chips and shredded tires are two examples of bulking agents. Wood chips are an excellent bulking agent because they also alter the moisture content and C:N ratio.

The composting of mortalities can be an economical and environmentally acceptable method. The process produces little odor and destroys harmful pathogens. Compost bins are typically about 5 feet (1.5 m) high, 5 feet (1.5 m) deep, and 8 feet (2.4 m) cross the front. The width across the front should be sized to accommodate the equipment used to load and unload the facility. To prevent spontaneous combustion and to allow for ease of monitoring, a bin height of no more than 6 feet (1.8 m) is recommended. The depth should also be sized to accommodate the equipment used. Rapid composting of mortalities occurs when the C:N ratio is maintained between 10 and 20. This is considerably lower than what is normally recommended for more traditional composting, because much of the nitrogen in the dead animal mass is not exposed on the surface. A lower C:N ratio is necessary to ensure rapid composting with elevated temperature to destroy pathogens. The moisture content of the initial compost mixture should be between 45 and 55%, by weight, to facilitate rapid decomposition. Composting of mortalities should remain aerobic at all times throughout the process. This is easily accomplished by layering the mortalities and amendments in the mix. Layers of such high porosity material as straw, wood chips and bark allow lateral movement of air in the compost mix.


Composting Bin

Cantrell Creek Trout Farm (NC)

Compost design requires knowledge of the characteristics of the aquaculture wastes and the amendments and bulking agents. The characteristics that are most important are moisture content, carbon content, nitrogen content and C:N ratio. The balance between the C:N ratio in the compost mixture is a critical factor for optimum microbial activity. These microbes multiply rapidly in the compost pile and consume carbon as a food source and nutrients to metabolize and build proteins. The C:N ratio of the compost mix should be maintained between 25 and 40 to 1. If the C:N ratio is low, a loss of nitrogen generally occurs through rapid decomposition and volatilization of the ammonia. If it is high, the composting time increases because the nitrogen becomes the limiting nutrient for growth. Moisture is required by the microbes to convert the carbon source to energy. Bacterial generally can tolerate moisture content as low as 12 to 15%. However at moisture contents of less than 40%, the rate of decomposition is slow. At greater than 60% moisture, the process turns from one that is aerobic to one that is anaerobic. Anaerobic composting decomposes more slowly and produces putrid odors. The determination of the compost mix design or retype is normally an iterative process of adjusting the C:N ratio and moisture content by the addition of amendments. If the C:N ratio is out of the acceptable range, then amendments are added to adjust it.


Land Application

• Liquid/Slurry Application– Solids are easily transferred and distributed when they are >1%

solids– Designed as a Slow Rate Land Treatment (crop irrigation)

• Thickened Sludge Application– Designed as a soil amendment or fertilizer (as part of a crop

nutrient management plan)– Applied from tanker trucks: surface spreading, incorporation,

direct injection


Land Application

When the solids content is less than 1%, solids and slurries are easily pumped and distributed

The simplest and most useful method of sludge disposal is to take advantage of it as a fertilizer for direct land application. Processed aquaculture sludge dry matter contains high levels of nitrogen and phosphorus, but negligible amounts of potassium. Nitrogen is mainly organically bound and has to be decomposed by microorganisms in order to become available for plants (Bergheim et al. 1993). When the solids content is less than 1%, solids and slurries are easily pumped and distributed. Thus, there are a variety of land application systems that can be used, including conventional irrigation via sprinklers and surface flooding. Climate constraints on crops and vegetation may require winter storage of the wastewater. Other methods include rapid infiltration of the wastewater by intermittent flooding of shallow basins in relatively coarse textured soils of rapid permeability. Thickened sludge (>5% solids) can be used as a soil amendment or fertilizer and applied from tanker trucks, by surface spreading with or without incorporation into the soil, and by direct injection into the soil.


Contract Hauling

By far the simplest method of sludge disposal is to have someone else haul it away.


Questions?

EUCALYPT SOWING AND SEEDFALL

Documents