3/29/2011 1 Wastewater Characterisation and Treatment Recommended text books: Wastewater Engineering – Metcalf and Eddy Standard Methods for Examination of Water and Wastewater Contact: Benoit Guieysse [email protected]RC.2.18 Lecture block outline The big picture: “Understanding the nature of wastewater is essential in the design and operation of collection, treatment, and reuse facilities – and in the engineering management of environmental quality” We need to know what’s in it before we can decide what to do with it! Characterisation Sampling Bio pollutants Chemical pollutants Physical pollutants Treatment Disposal Tertiary Secondary Primary
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
3/29/2011
1
Wastewater Characterisation and Treatment
Recommended text books:
Wastewater Engineering – Metcalf and Eddy
Standard Methods for Examination of Water and Wastewater
A solid is a chemical or particle that is solid in a dry form under “normal condition of temperature and pressure”.
In water, a solid is “anything” that would remain after the water is being evaporated.
In water, a solid can be found dissolved or in suspension. The dissolved solid fraction (TDS) can pass through a 45µm pore size filter whereas the suspended solid (TSS) is retained by the filter.
3/29/2011
5
Solids size
1000nm 100nm 1nm
molecularcolloidalfinecoarse
Sizes of solids; source: sawyer, 1994.
Organic waste bacteria proteinsviruses
Colloidal materials are very fine solids of 0.001 – 0.5 μm that
cannot be removed by simple sedimentation process
Solids fractionation
Total solids content (TS): all the matter that remains as residue upon evaporation at 103-105oC
Settleable solids: settle to the bottom of a cone shaped container in 1hr (mL/L)
Total suspended solids (TSS): are in suspension in the liquid phase – ie, they are removed from the liquid by filtration (mg TSS/L)
Volatile suspended solids (VSS): are driven off at temp of 550oC(mg VSS/L)
3/29/2011
6
Sample Settleablesolids
FSSeg.
sand
TSS
DFSeg.
NaCl
TFSTVS
DVSeg.
sugar
VSSeg.
bacteria
TDS
Filter(glass fibre)
ImhoffCone
Oven105oC TS
Oven550oC
Oven550oC
Oven550oC
filtrate
Solids map
FiltrationSuspended solids include bacteria as well as waste material
Caught in the filter = suspended solidmeasured in mg SS/L
The filter needs to be dry before and after filtration!
3/29/2011
7
VolatisationVSS is an indication of bacteria/biomass content in the wastewater – important for monitoring biological wastewater treatment
Organic material will oxidise as gas at temp of 550 +/- 50oC – inorganic fraction remains as ashmeasured in mg VSS/L
Furnace is used to generate very high temperature – be careful!
Settable solids
Imhoff cone
solids accumulate in the bottom, measured in mL/L
Important measure of the quantity of material that can be removed by primary sedimentation
3/29/2011
8
Summary sheet for solids – Most important fractions are TS, TSS, VSS, TDS
Test DescriptionTotal solids (TS) Residue after a wastewater sample has been
evaporated and dried (103 to 105°C, 24h).
Total volatile solids Solids volatilized after the incineration (500°C) of theTS fraction
Total fixed solids Residue remaining after incineration of the TS (TS =TVS + TFS)
Total suspended solids (TSS) Portion of the TS retained of a filter of specified poresize
Volatile suspended solids (VSS) Volatile fraction of the TSS that has been incinerated
Fixed suspended solids (FSS) FSS = TSS – VSS
Total dissolved solids (TDS) TDS = TS – TSS. This fraction also comprises colloids,which size typically range from 0.001 to 1 µm.
Total volatile dissolved solids (VDS) Volatile fraction of TDS
Fixed dissolved solids (FDS) FDS = TDS – VDS
Settleable solids Suspended solids that will settle out of suspensionwithin a specified amount of time.
3.3. Turbidity
Turbidity is a measure of light-transmitting properties – it is a test of the
quality of effluent with respect to colloidal and residual suspended matter
Issues: High degree of variability observed depending on the light source
& varying light adsorbing properties of the suspended material
Difficult to compare turbidity values reported in literature – but turbidity
meters can be used to monitor relative plant performance
3/29/2011
9
Turbidity
1 NTU = 1 Formazin Turbidity Unit (FTU) for a given apparatus.
3.4. Conductivity
Electrical Conductivity (EC) is the measure of the ability of a solution to conduct
an electrical current. EC is related to total dissolved solids (as it is related to the
concentration of ions in solution).
TDS (mg/L) ≈ EC (millisiemens / m) x 10 x (0.55 – 0.70)
EC is used as a measure of salinity so it is an important parameter for
determining if water is suitable for irrigation
3/29/2011
10
Temperature :
1. Affects the reaction rate
2. Affects the solubility of
gases
3.5. Temperature
Temp. of domestic WWT systems can vary with seasons and can be
directly related to process operations
Oxygen solubility (and with it Dissolved Oxygen – DO) decreases with increasing temperature
3/29/2011
11
4. Chemical Properties
pH
Alkalinity
Nitrogen
Phosphorus
Metals
Soluble gases
Organics
4.1. pHpH is related to the hydrogen ion
concentration, it is defined as:
pH = -log [H+] = log(1/[H+])
The pH of pure water is equal to 7.
Solutions with pH < 7 are acidic,
solutions with pH > 7 are basic.
pH is naturally influenced by CO2
concentration as CO2 dissolves and
forms carbonic acid
3/29/2011
12
4.1. Alkalinity
The alkalinity of water is a measure of its capacity to neutralize acids (buffer
capacity)
Bicarbonate (HCO3-) represents the major form of alkalinity in natural water
(pH around 7), because it is formed upon the reaction of CO2 with calcium (or
The same reactions also explain the presence of Ca2+ and Mg2+ in water, which
are responsible for the hardness of the water.
[Carbonate = CO32- / bicarbonate = HCO3
- / carbonic acid = H2CO3]
[OH- and CO32- only contribute significantly to alkalinity for pH > 9-10]
4.2. Nitrogen
Nitrogen is a fertilising agent. Elevatedquantities of inorganic N can cause algalblooms. Nitrogen is not often limiting in freshwater but is often limiting in sea water.
Essential to the growth of algae and other biological organisms – excessive
concentrations can cause excessive growth.
Interest in reducing N loads in effluents (typical domestic N content 20-50 mg
nN/L)
N is usually found in organic compounds (proteins) and inorganic compounds
such as ammonia (NH4+ or NH3 depending on the pH), nitrite, and nitrate.
3/29/2011
13
Nitrogen summary
MOST REDUCED NH3 → NO2 →.NO3 MOST OXIDISED
Form NotesAmmonia NH3 In equilibrium with NH4
+ (NH4+ ↔ NH3 + H+)
In wastewater, with pH less than 8, most is present as NH4+
Typical range in domestic WW is 15-40 mg/L. Much higher inagricultural WW and leachate.
Measured by colorimetry, titrimetrically or by ion specific electrodes.
Nitrate NO3- Most oxidised form of nitrogen. High concs are harmful to human
health (blue baby syndrome).
Typical range in treated effluents is 15-20mg/L.
Measured by colorimetry or by ion specific electrodes.