Session 3. Water Pollution Control Techniques

Transcription

1 Session 3 Water Pollution Control Techniques

2 Contents 1. What is water pollution? 2. Pollutants and their characterisation 3. Wastewater types 4. Receiving waters and discharge consents 5. Options hierarchy 6. Integrated on-site treatment 7. Summary 8. IPPC application requirements 2

3 What is Water Pollution? Natural water (e.g. rivers, sea, groundwater etc) contain many dissolved and suspended substances Water becomes polluted when contaminants are added at a rate which exceeds natural breakdown or dilution processes when the contamination is toxic to plant or animal life The severity of pollution depends on: Toxicity Persistence Bioaccumulation (the ability of a substance to be accumulated within the body of an organism. 3

4 Principal Pollutants Soluble organics - these deplete oxygen Suspended solids - these cause turbidity, impair aquatic life and indirectly deplete oxygen Trace organics (such as phenols) - these cause taste and odours problems and increase the cost of water treatment. Can have a high BOD. Nitrogen and phosphorous these cause eutrophication, leading to high turbidity and depletion of oxygen Heavy metals, cyanides and toxic organics - these may be acutely toxic Oil and floating material - these produce unsightly conditions and can block light, and deplete oxygen Colour and turbidity - these present aesthetic problems and restrict light penetration into the water 4

5 Main Polluting Substances Organohalogen compounds and related substances Organophosphate compounds Organotin compounds Substances possessing carcinogenic or mutagenic properties Persistent hydrocarbons Persistent and bioaccumulable organic toxic substances Cyanides 5

6 Main Polluting Substances Metals and their compounds Arsenic and its compounds Biocides and plant health products Materials in suspension Substances which contribute to eutrophication (particularly nitrates and phosphates) substances which have an unfavourable influence on oxygen balance (measured by BOD, COD para) Tip: useful web site, contains chemical fact sheets: 6

7 Wastewater Characterisation Key parameters for effluent quality: Temperature and ph (acidity/alkalinity) BOD 5 at 20 o C (Biochemical Oxygen Demand) COD (Chemical Oxygen Demand) Suspended solids Nitrogen and phosphorus (eutrophication substances) Fat, oil and grease (FOG) Specific contaminants: Toxic metals (Mercury, Cadmium, Chromium (VI), Lead, Arsenic) Phytotoxic elements (copper, manganese, nickel, tin, zinc, iron, boron) Other - Cyanide, Phenol, Chlorine, 7

8 BOD and COD Biochemical oxygen demand test: Determines the amount of oxygen needed for microorganisms to bio-degrade organic waste into nonharmful matter e.g.. CO 2, N 2, H 2 O Chemical oxygen demand test: Determines the amount of oxygen needed for chemical oxidation of organic and in-organic compounds 8

9 Wastewater types There are many sources of wastewater from industrial installations: Process activities Washing and cooling processes (heat exchangers, compressors) Air emission control systems Rain and storm - carried as surface water and then drain Accidental emissions/releases Mopping up operation (after a spill) Fire fighting 9

10 Water discharges Sewer River Estuary Coastal waters These four outlets are dealt with in the BAT assessment methodology given in H1 10

11 Comparison of discharge consents Sewer discharge mg/l COD Licensed by water companies River and estuary discharge ~20 mg/l SS; ~30 mg/l BOD Licensed by Environment Agency Coastal waters (and Land application) Consents vary Licensed by Ministry of Agriculture Fisheries and Food MAFF 11

12 Waste hierarchy Prevent Reduce/minimise Re-use Recycle Dispose Best/Cheapest Worst/Expensive 12

13 Prevention, minimisation and control For each wastewater stream the following questions should be addressed: 1. Can the quantity and contamination level be reduced or eliminated by process optimisation? 2. Can the streams from different parts of the plant be collected separately? 3. Can the streams be reused or recycled (after treatment)? 4. Should any of the streams be treated separately or jointly with other streams? 13

14 Key flows in wastewater treatment Waste water Physical separation Sludge treatment Disposal of residue Treatment of relatively persistent pollutants Treatment of biodegradable constituents Recipient water 14

15 Physical Separation - (primary/secondary) Aimed at suspended solids and insoluble liquids: Grit separation Coagulation/flocculation Sedimentation Air flotation Coarse filtration Membrane filtration micro-filtration (MF) & ultra-filtration (UF) Oil water separation 15

16 Treatment of Relatively Persistent Pollutants - (secondary/tertiary) Aimed at the removal of inorganic and poor or nonbiodegradable components: Precipitation Crystallisation Oxidation (chemical, wet air, super critical water) Chemical reduction Chemical hydrolysis Nano-filtration, reverse osmosis Other: adsorption, ion exchange, extraction, distillation/stripping, evaporation, incineration 16

17 Biological Treatment - (secondary/tertiary) Aimed at the removal of biodegradable soluble content and selective metals and sulphur: Anaerobic treatment anaerobic contact process, upflow anaerobic sludge blanket (UASB) process, fixed bed filter process, expanded or fluidised bed anaerobic process Aerobic treatment activated sludge process, trickling/percolating filter process, expanded bed process, biological N&P removal process 17

18 Sludge Treatment Aimed at treatment, recycling and/or disposal: Bio-solids destruction (by aerobic or anaerobic digestion process) Solids concentration (thickening) Solids de-watering (drying beds, centrifugation, vacuum filtration) Organic solids destruction (incineration) Disposal (landfill) 18

19 Factors influencing design of on-site treatment system WASTEWATER WASTEWATER CHARACTERISTICS CHARACTERISTICS SITE-SPECIFIC SITE-SPECIFIC CONSTRAINTS CONSTRAINTS e.g. e.g. Land Land area, area, proximity proximity to to residential residential area area WASTEWATER WASTEWATER TREATMENT TREATMENT SYSTEM SYSTEM FLOW AND LOAD BALANCING FAVOURABLE BIOCHEMICAL CHARACTERISTICS (ph, C:N:P adjustments) SLUDGE SLUDGE OUTLETS OUTLETS TREATED TREATED EFFLUENT EFFLUENT OUTLETS OUTLETS 19

20 On-site treatment system Dedicated wastewater treatment facilities may vary: simple traps (sumps, silt traps, oil interceptors) simple treatment (e.g. neutralisation tank) complex treatment (full wastewater treatment plant) The treatment technique chosen must be appropriate to the types of contamination, on-site constraints and environmental benefits to be gained 20

21 Summary Water pollution control comprises: Water pollution prevention and minimisation by design, operation and management techniques Choice of best available on-site solution that depends on pollution components, wastewater generation patterns, discharge consents, sludge outlets and site specific constraints. 21

22 The IPPC application requirements The application should include: BAT in water use and minimisation BAT in wastewater management, including in treatment plant (WWTP) Description of the WWTP Site drainage map Justification for not cleaning any effluent for reuse main chemical constituents of the effluents (especially, make up of the COD) and assessment for their fate in the aquatic environment identification of the toxic substances and their symptoms and controls to reduce their impacts Performance guarantees of the WWTP 22

23 BAT considerations (1) The operator should ensure that procedures are/will be in place to prevent or reduce the emissions to water and justify where any of the measures are not employed, considering: the sources, direction and destination of all drains. all sumps and storage vessels. engineered systems that ensure leakages from pipes etc are minimised and where these could occur (and be detected), particularly where hazardous substances are involved). any secondary containment and/or leakage detection. an inspection and maintenance programme (e.g. pressure tests, CCTV). 23

24 BAT Considerations (2) Description of the design, construction and condition of the surfacing of all operational areas Inspection and maintenance programme of all impervious surfaces and spill containment kerbs Bunds should be provided for all tanks containing liquids which have a potential impact on the environment. 24

25 BAT Considerations (3) Bunds should: be impermeable and resistant to the stored materials have no outlet but drain to a blind collection point have pipework routed within bunded areas with no penetration of the surfaces be designed to catch leaks from tanks and fittings have a capacity of 110% of the largest tank or 25% of the total tankage, whichever is the greater be subject to regular visual inspection or alarm system have fill points within the bund or provide adequate containment 25

26 Overall BAT issues Water use should be minimised and wastewaters reused or recycled, where possible The excess wastewaters are likely to need treatment (to meet the requirements of the BAT and statutory and non statutory objectives) Collection and transfer of wastewaters should be engineered so that all streams can be led to the WWTP All emissions off-site should be controlled to avoid a breach of the water quality standards 26

27 Further BAT stuff In addition to the BAT on water use minimisation and WWTP, the following should be examined: management management system (ISO 14001, EMAS) staff numbers training personnel competencies working methods maintenance records and monitoring of any releases 27

28 Waste Water Treatment - Example 28