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Advanced Onsite Wastewater Treatment Technologies and Nitrogen Removal

Apr 12, 2017

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Environment

pete-sabo

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Advanced Onsite Wastewater Treatment Technologies for Nitrogen Removal

Pete SaboHydro-Action

Overview

Nitrogen in the EnvironmentWastewater Characteristics Nitrogen LoadingImpacts of Nitrogen PollutionOnsite Wastewater Treatment Technologies That Reduce Nitrogen LoadingTypes of Technologies in Suffolk County

SourcesOakley, S. 2005. Onsite Nitrogen Removal Text. in (M.A. Gross and N.E. Deal, eds.) University Curriculum Development for Decentralized Wastewater Management. National Decentralized Water Resources Capacity Development Project. University of Arkansas, Fayetteville, AR.Suffolk County OfficialsPeconic Green Growth OrganizationUS EPANOWRA

Nitrogen

78% of Earths atmosphere is Nitrogen gasNatural occurring in the environmentNitrogen is transformed in the environment through multiple methods: fixation, ammonification, synthesis, nitrification, and denitrification (US EPA, 1993).

Nitrogen & Wastewater PollutionRange of Concentrations Cited in Literature, mg/L

ConstituentWithout Effluent Filter With Effluent FilterBOD5 (mg/l)7 to 480100 to 140TKN (mg/l)9 to12550 to 90Alkalinity (as CaCO3) (mg/l)---70 to 594

Wastewater PollutionBasic calculations: Family of 4; conventional septic; acre lot

Total of 50 lbs/year (Hantszche and Finnemore, 1992)

Comparing it to natural biological uptake: acre of Bermuda grass can absorb 50 lbs/year Nitrogen (WEF, 2001).

Wastewater Pollution

Build up of nitrates in groundwater is the most significant long term consequence of onsite wastewater disposal (Hantzsche and Finnemore, 1992)

Wastewater Factors69% of Total Nitrogen loading from septic tanks & cesspools (source: Kinney, E. L. and Valiela, 2011)

Effluent Disposal FactorsLocation of plants roots, soil bacteria, all soil biotaEffluent being distributed below the zone where plants and soil biota can absorb nitrogenCloser to the water table and aquaferNot evenly distributed either; dependent on water consumption of the homeGreat variation between per capita GPD, BOD, and nitrogen effluent

Wastewater FactorsUrban density is largest factorHigher density, less ability for plants to absorb Nitrogen (Gold and Sims, 2000; County of Butte, 1998; Hantzsche and Finnemore, 1992).

QUESTION #1What is the biggest long term concern of onsite wastewater treatment?

QUESTION #2What is the most significant factor for wastewater disposal?

Nitrogen LoadingAverage per capita Nitrogen mass loading of wastewater 4 to 18 lbs per capita1.1 million people in Suffolk County with onsite wastewater systems

360,000 homes with onsite treatment209,000 priority (proximity to water)252,000 without septic tank (pre-1972)

Existing Infrastructure26% (388,180) Sewered194 WWTPNeed 550 more

74% (1.1 mil) UnseweredCesspoolsSeptic Tanks

QUESTION #3How many homes in Long Island utilize onsite wastewater treatment?

Human Health Impacts

Human Health ImpactsMethemoglobinemiaCancerBirth Defects

MethemoglobinemiaStrong Evidence / Positive Correlation

Definition: Lack of sufficient oxygen in bloodNitrate ingested in infants less than 6 monthsHemoglobin to Methemoglobin Reduced oxygen carrying capacity of circulatory systemBlue Baby Syndrome

CarcinogenesisMedium Evidence/ Some Positive Correlation

Definition: Cancer-causingHigh nitrate levels in drinking waterFormation of nitrosamines (converted nitrates/nitrite), which several are carcinogenicTested on animals and proven correlation

Birth DefectsWeak Evidence/ Lack of True Positive Correlation

DefinitionStatistically significant increase in congenital malformations associated with nitrate-rich well waterLimited evidence/studies

QUESTION #4What are the human health concerns of nitrogen pollution?

Environmental Health Impacts

Ecological ImpactsEutrophicationOxygen Demand though NitrificationAmmonia Toxicity to Aquatic Organisms

EutrophicationExcess nitrogen can cause the stimulation of growth, resulting in algal blooms or overgrowth of aquatic plants

Dissolved oxygen depletion in the water: fish kills, aquatic species like shell fish, oysters, turtles, etc. die, decomposition and odors, biomass accumulation,

Oxygen Demand from NitrificationNitrogenous biochemical oxygen demand (NBOD): Nitrification requires high levels of oxygen and will utilize as much as possible

Greater demand on oxygen than carbonaceous biochemical oxygen demand

Ammonia Toxicity to Aquatic OrganismsNitrogen in the form, NH3-N can be toxic to aquatic organisms and kill them

QUESTION #4What are the three environmental impacts of nitrogen pollution?

Onsite Wastewater TreatmentPrimary TreatmentCollectionSedimentationEffluent Disposal

Advanced Onsite Wastewater TreatmentPrimary TreatmentCollectionSedimentationSecondary TreatmentAerobic TreatmentFiltrationEffluent Disposal

Onsite Wastewater Treatment

How a Septic Tank WorksCollection: Collects the wastewater into a proportionally sized vessel where sedimentation and anaerobic digestion occur

Anaerobic digestion: In an oxygen deprived environment, anaerobic bacteria will treat a small percentage of the total wastewater mass, nutrients, etc. including Nitrogen

How a Septic Tank WorksSedimentation and Flotation: Flotation occurs as well: mass density less than water floats, such as fats, oils, greases, etc. which will coagulate and form a scum layer that sits above the septic tank outlet

Septic tanks can remove 10-30% of Nitrogen mostly through settling the BOD solids and organic material

Advanced OWTSPost-tank treatment can include aerobic (with oxygen) or anaerobic (with no or low oxygen) biological treatment in:suspended reactorsfixed-film reactors, physical/chemical treatment, soil infiltration, fixed-media filtrationdisinfection chlorination -> UV Suspended GrowthAttached Growth(Source: US EPA, 2002)

Nitrogen RemovalSequential Nitrification -> Denitrification Aerobic bacteria process first used to remove BOD (solids) and nitrify organic Nitrogen and NH4; need to send aerobically treated wastewater to an anoxic environment

Nitrogen RemovalSequential Nitrification -> Denitrification Then in an oxygen deprived environment (anoxic zone), denitrifiying bacteria will further metabolize the organic-N and NH4 into NO3 to N2 gas Using wastewater as the carbon source or including a technological feature that supplements the anoxic zone with external carbon source

Nitrogen RemovalBiological nitrification/denitrification is the only process that has been demonstrated to be feasible, both economically and technically, for onsite nitrogen removal (the same can be said for large-scale wastewater treatment plants)(Whitmeyer, et al., 1991)

Nitrogen RemovalNitrification requires high dissolved oxygen due to the high nitrogenous biochemical oxygen demand of nitrification (NBOD).

If theres not enough oxygen, nitrification will be limited, and thus overall denitrification and total Nitrogen removal will be limited as well.

QUESTION #7What is the only process thats economically & technically feasible to remove nitrogen?

Nitrogen RemovalInfluent wastewater can be used as the carbon source by recycling nitrified effluent to an anoxic reactor that precedes the aerobic nitrification reactor

Operating alternating aerobic/anoxic zones on one reactor (sequencing batch reactor), or conveying the flow sequentially through alternating aerobic/anoxic zones (US EPA, 1993).

Denitrification reactors can be designed as suspended-growth attached-growth processes

Nitrogen RemovalNitrifying bacteria reproduce significantly slower than heterotrophic bacteria, thus nitrification is controlled by heterotrophic oxidation of CBOD;

High organic loading of CBOD will lead to heterotrophic bacteria dominating the environment of the biofilm.

This affects the rates of nitrification and overall reduction in Total N.

Sufficient capacity and detention time must be engineered in order to allow the nitrifying bacteria time to develop.

Nitrogen RemovalTemperature: Cold temperatures affect overall nitrogen removal: colder temperatures require longer cell residence times in suspended-growth systems and lower hydraulic loading rates in attached-growth systems due to slower growth rates of nitrifying bacteria.

Denitrification rates can be significantly affected by temperature drops below 20 C, with the denitrification rate at 10 C ranging from 20% to 40% of the rate at 20C (US EPA, 1993).

Suspended GrowthBiological treatment processes in which the microorganisms responsible for treatment are maintained in suspension within the liquid, usually through mechanical or diffused-air aeration (Metcalf & Eddy, 1991).Concentration of dissolved oxygen (DO) has significant effect on nitrification rates2.0 mg/L is the targetAerobic Treatment UnitsSequencing Batch Reactors

Suspended GrowthAerobic Units (with pulse aeration)Extended aeration activated sludge systems in which aeration is periodically stopped or pulsed to promote denitrification.Continuous aeration38-61% Nitrogen Removal; 37 to 60 mg/L

Suspended GrowthSequencing Batch Reactorsfill-and-draw, and alternating aerobic and anoxic cycles, are created within a single reactor60% removal; 15.5 mg/L average influent TKN concentration of 38.4 mg/L (Ayres Associates, 1998).

Attached GrowthBiological treatment processes in which the microorganisms responsible for treatment are attached to an inert medium such as sand, gravel, or plastic media, and can include either submerged or nonsubmerged processes (Crites and Tchobanoglous, 1998; Metcalf & Eddy, 1991).

Surface area is crucial to the media in order to maximize oxygen transfer rates and maintain sufficient nitrification levels beyond the heterotrophic bacteria rates of growth.

Attached GrowthSingle Pass Sand Filters (SPSF)Most studied of all proposed nitrogen removal technologiesCombination of CBOD removal and nitrification within the sand medium at low organic loadingsDenitrification within anoxic microenvironments in the sand8% to 50% removalSPSF systems will always be denitrification-limited due to the lack of availability of both a carbon source and anoxic conditions.

Attached GrowthRecirculating Sand/Gravel Filters (RSF)Well studied15% to 84% removal High nitrification rates and consistently higher denitrification rates than SPSFs because the nitrified effluent can be recycled back to a recirculation tank where it mixes with wastewater from the septic tank, thus using the incoming wastewater as a carbon source.Sludge accumulation in the rock tank, however, can potentially cause serious operation and maintenance problems.

Technology TypeTotal-N Removal %Effluent Total-N mg/LSuspended GrowthAerobic units w/ pulse aeration25-6137-60Sequencing batch reactor6015.5Attached GrowthSingle-Pass Sand Filters (SPSF)8-5030-65Recirculating Sand/Gravel Filters (RSF)15-8410-47Multi-Pass Textile Filters 14-3114-17RSF with Anoxic Filter40-907-23RSF with Anoxic Filter and External Carbon Source74-8010-13

Onsite Technologies >85% NitrificationProcessEffectivenessOnsite StatusIn Suffolk CountySuspended GrowthAerobic UnitsPotentialInsufficient design and performance data. Operation and Maintenance unknown.YesAttached GrowthSingle Pass Sand Filters (SPSF)ProvenWidespread use. Need more design and performance data.Recirculating Sand FiltersProvenWidespread use. Need more design and performance data.Single-Pass Textile FiltersPotentialLimited data to date. Probably similar to SPSF. Need design data for organic loadings nitrification.Multi-pass Textile FiltersPotentialLimited data to date. Need design and performance data.Yes

SUMMARY OF INNOVATIVE/ALTERNATIVE ONSITE WASTEWATER TREATMENT FOR SINGLE FAMILY HOMES AND SMALL COMMERCIAL USES CompanyName of SystemSuffolk Cty. StatusNSF 245 or EPA 3rd Party TestNSF 350 reuse NSF 41 Dry TestSeasonal Uneven Use No Possible GoodTN mg/L (lower is better)TN % ReduceOrganic/ Food loads Yes No OptionH-20 Vehicular loading Yes No OptionFunction in Power Outage Yes/ No Option2Capital CostEnergy Cost/ month $0.18/ kWhReplace septic tank Yes/No OptionReplace leaching PitFootprint SFDepth Ft1More (link to Fact Page)TRICKLING FILTER / FIXED FILM (aerobic)/PACKED BEDAquaPointBioClere Model 16/12YP11-1657-70%NNY$$$$19 NN204-7'Link FP1SeptiTechSeptiTech / STAARPilot 2YP1175%NON$$$$$29 NN514.25Link FP2EliminiteC-SeriesYG70% - 90%YON$$$*$5-11ON966-7'Link FP4Orenco SystemsAdvanTex AX20Pilot 1YG14-1663- 82%NNN$$$*$2.60-$5.00NN200-2.6'Link FP5Orenco SystemsAdvanTex AX-20RTPilot 1YG14-1663-82%NNN$$$*$5 NN448.33'Link FP6Premier Tech Aqua (div, Premier Tech Technologies Ltd.)Ecoflo CoCo Filter ECDn Model Series Pilot 2YG

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