Treatment of Wastes in Industry

1. Treatment of Wastes in Industry

2. METHODS FOR THE DETERMINATION OF ORGANIC MATTER CONTENT IN WASTE WATERS • If waste water discharged into a natural water is rich in degradable organic matter, large numbers of aerobic microorganisms will develop to break down the organic matter. • Use up the available oxygen and as a consequence fish and other aquatic life will die. • Anaerobic bacteria will develop following the exhaustion of oxygen. • Result in foul odors.

3. Dissolved Oxygen • The Biological or Biochemical Oxygen Demand (BOD) Tests • Permanganate Value (PV) Test • Chemical Oxygen Demand (COD) • Total Organic Carbon (TOC) • Total Suspended Solids (TSS) • Volatile Suspended Solids (VSS)

4. Dissolved Oxygen • Dissolved oxygen is one of the most important means of determining the organic matter content of waters. • The heavier the amount of degradable material present in water, the greater the growth of aerobic organisms and hence the less the oxygen content. • The Winkler method is widely used for determining the oxygen in water. • Membrane electrodes are now available for the same purpose.

5. The Biological or Biochemical Oxygen Demand (BOD) Tests • It is a measure of the oxygen required to decompose the organic matter in a body of water over a five-day period at 20°C. • In carrying out the test, two 250-300 ml bottles are filled with water whose BOD is to be determined. The oxygen content of one is determined immediately by the Winkler method and in the other at the end of five days incubation at 20°C. The difference between the two is the BOD.

6. Many industrial wastes contain materials which are either difficult to degrade or which may even be toxic to the organisms. • In such cases an inoculum capable of degrading the materials must be developed by enrichment and introduced into the bottles.

7. Permanganate Value (PV) Test • Determines the amount of oxygen used up by a sample in four hours. • It gives an idea of the oxidizable materials present in water. • The method records the oxidation of organic materials such as phenol and aniline as well as those of sulfide, thiosulfate, and thiocyanate and would be useful in some industries. • However because oxidation is incomplete it is not favored by some workers.

8. Chemical Oxygen Demand (COD) • The total oxygen consumed by the chemical oxidation of that portion of organic materials in water which can be oxidized by a strong chemical oxidant. • It is a more rapid test than BOD, the method can be used for a wider variety of wastes. • Furthermore, when materials toxic to bacteria are present it is perhaps the best method available. • Its major disadvantage is that bulky equipment and hot concentrated sulfuric acid are used.

9. Total Organic Carbon (TOC) • Total organic carbon provides a speedy and convenient way of determining the degree of organic contamination. • A carbon analyzer using an infrared detection system is used • The amount of carbon will be expressed in mg/L. • TOC provides a more direct expression of the organic chemical content of water than BOD or COD.

10. Total Suspended Solids (TSS) • Total Solids include both total suspended solids, the portion of total solids retained by a filter and total dissolved solids, the portion that passes through a filter. • Total solids can be measured by evaporating a water sample in a weighed dish, and then drying the residue in an oven at 103 to 105°C. • To measure total suspended solids (TSS), the water sample is filtered through a preweighed filter. • The residue retained on the filter is dried in an oven at 103 to 105°C. • TSS can also be measured by analyzing for total solids and subtracting total dissolved solids.

11. Volatile Suspended Solids (VSS) • Volatile suspended solids (VSS) are those solids (mg/liter) which can be oxidized to gas at 550°C. • Most organic compounds are oxidized to CO2 and H2O at that temperature; • Inorganic compounds remain as ash.

12. WASTES FROM MAJOR INDUSTRIES Typical Components of an Oil Refinery Waste Water

13. Typical Effluent Loads from Pulp and Paper Manufacture

14. Typical Effluent Loads from Food industries

15. SYSTEMS FOR THE TREATMENT OF WASTES (i) The degradable organic compounds in the waste water (carbohydrates, proteins, fats, etc.) are broken down by aerobic micro-organisms mainly bacteria and to some extent, fungi. • The result is an effluent with a drastically reduced organic matter content. (ii) The materials difficult to digest form a sludge which must be removed from time to time and which is also treated separately. • Aerobic breakdown of raw waste-water and anaerobic breakdown of sludge.

16. Aerobic Breakdown of Raw Waste Waters • The activated sludge system • The trickling filter • Rotating discs

17. The activated sludge system (a) It uses a complex population of microorganisms of bacteria and protozoa; (b) This community of microorganisms has to cope with an uncontrollably diverse range of organic and inorganic compounds some of which may be toxic to the organisms. (c) The microorganisms occur in discreet aggregates known as flocs (d) Some of the settled biomass is recycled as ‘returned activated sludge’ inoculate the incoming raw sewage because it contains a community of organisms adapted to the incoming sewage. (e) The solid undigested sludge may be further treated into economically valuable products.

18. Organisms involved in the activated sludge process • The organisms involved are bacteria and ciliates (protozoa). • A wide range of bacteria are involved, including Pseudomonas, Achromobacter, Flavobacterium to name a few.

19. Efficiency of activated sludge treatments • The efficiency of any system is usually determined by a reduction in the BOD of the waste water before and after treatment. • Efficiency depends on the amount of aeration, and the contact time between the sludge and the raw waste water. • Thus in conventional activated sludge plants the contact time is about 10 hours, after which 90-95% of the BOD is removed. • When the contact time is less (in the high-rate treatment) BOD removal is 60-70% and the sludge produced is more.

20. With longer contact time, say several days, BOD reduction is over 95% and sludge extremely low. • In the closed tank system or where there is great oxygen solubility, contact time could be as short as 1 hour but with up to 90% BOD reduction along with substantially reduced sludge.

21. The trickling filter • No sludge is returned to the incoming waste water. • Rather the waste water is sprayed uniformly by a rotating distributor on a bed of rocks 6-10 ft deep. • The water percolates over the rocks within the bed which are 1-4 ft in diameter and is collected in an under-drain. • The liquid is then collected from the under drain and allowed in a sedimentation tank which is an integral component of the trickling filter. • The sludge from the sedimentation tank is removed from time to time.

22. Section through Trickling Filter Bed

23. Microbiology of the trickling filter • A coating of microorganisms form on the stones as the waste water trickles down the filter and these organisms break-down the waste. • Fungi, algae, protozoa and bacteria form on the rocks. • As the filter ages the aerobic bacteria which are responsible for the breakdown of the organic matter become impeded, • The system becomes inefficient and flies and obnoxious smells may result. • The microbial coating sloughs off from time to time.

24. Rotating discs • Consist of closely packed discs about 10 ft in diameter and 1 inch apart. • Discs made of plastic or metal may number up to 50 or more and are mounted on a horizontal shaft which rotates slowly, at a rate of about 0.5-15 revolutions per min. • During the rotation, 40-50% of the area of the discs is immersed in liquid at a time.

25. A slime of microorganisms, which decompose the wastes in the water, builds up on the discs. • When the slime is too heavy, it sloughs off and is separated from the liquid in a clarifier. • It has a short contact time and produces little sludge. • The rotating disc system can be seen as a modification of the tricking filter in which the waste water is spread on rotating discs rather than on a bed of rocks.

26. Structure of Rotating Discs (Rotating Biological Contactor)

27. TREATMENT OF THE SLUDGE: ANAEROBIC BREAKDOWN OF SLUDGE • Sludge consists of microorganisms and those materials which are not readily degradable particularly cellulose. • The solids do not exceed 5%. • The goals of sludge treatment are: • to stabilize the sludge and reduce odors, • remove some of the water and reduce volume, • decompose some of the organic matter and reduce volume, • kill disease causing organisms and disinfect the sludge. • Caustic chemicals can be added to sludge or it may be heat treated to kill disease-causing organisms. • Following treatment, liquid and cake sludges are usually spread on fields, returning organic matter and nutrients to the soil.

28. Anaerobic Digestion of Sludge • The commonest method of treating sludge however is by anaerobic digestion. • By allowing the sludge to decompose in digesters under controlled conditions for several weeks. • Digesters themselves are closed tanks with provision for mild agitation, and the introduction of sludge and release of gases. • About 50% of the organic matter is broken down to gas, mostly methane.

29. Amino acids, sugars alcohols are also produced. The broken-down sludge may then be de-watered and disposed of by any of the methods described above. Sludge so treated is less offensive and consequently easier to handle. • Organisms responsible for sludge breakdown are sensitive to pH values outside 7-8, heavy metals, and detergents and these should not be introduced into digesters. • Methane gas is also produced and this may sometimes be collected and used as a source of energy.

30. Example : Waste Water Treatment • Primary Treatment • physical separations, removing large objects • Secondary Treatment • reduce the organic load of the sewage to acceptable levels before releasing it to natural waterways • Tertiary Treatment • a physicochemical process employing precipitation, filtration, and chlorination to sharply reduce the levels of inorganic nutrients, especially phosphate and nitrate, from the final effluents

32. Example : Waste Water Treatment Technology

33. Anoxic sludge digester (only the top of the tank is shown, the remainder is underground. Inner working of a sludge digestor

34. 2 stage digestion

35. Major microbial processes occurring during sludge digestion

36. Anaerobic Wastewater Treatment • Breweries • Dairy and cheese production • Fish processing • Leachate treatment • Pulp/paper • Meatpacking • Distilleries • Municipal waste

37. Anaerobic Wastewater Treatment • Similar configurations to activated sludge, aerobic reactors, but no oxygen. • Used more with industrial wastewaters • Intermittent flows • High COD • Uses less energy, makes less sludge, makes CH4 (energy), but….. • Biomass grows slowly, acidifies, partial treatment, no extra P or N removal

38. Anaerobic Wastewater Treatment: Considerations • Mesophilic (25 to 35°C) conditions advantageous • Long Retention Time: e.g. 20 days at 30° C • May need to add CaCO3 to buffer • May need to add nutrients • Sensitive to • Toxic metals and organics • Ammonia

39. Microbiology of Anaerobic Treatment • CO2 or organics are e- acceptors • C is from CO2 or organic compounds • Energy is from organic compounds or H2 • Slow growing bacteria

40. Conversions and operative groups of bacteria in anaerobic digestion.

41. Anaerobic digester microbiology • 1: extracellular hydrolysis (e.g. cellulase) • 2: fermentation leading to organic acids, acetate, CO2 and H2 • 3: fermentation leading to acetic acid (CH3COOH), H2 and O2 • 4: methanogenesis leading to CH4, CO2 and H2O

42. Methanogenesis • By methanogens; which are archaea • By either • Hydrogen utilizers (1/3) • Acetate-splitters (2/3) • pH sensitive (7 – 7.2) • Lowers H2 which facilitates acetate formers

43. What happens in digestion? • Stabilization • Reduce pathogen content • Reduce odors • Volatile solids reduction (about 60%) • Gas production (70% CH4, 30% CO2) (anaerobic only)

44. Biosolids Disposal • Land application: fertilizer (bulk or bagged) • Surface disposal: dedicated lagoons or other sites • Pathogen and vector reduction • Class A: low pathogens and treatment choices specified (nurseries, gardens, golf courses) • Class B: lesser treatment (agriculture, landfill) • incineration

45. Aerobic sewage treatment processes: trickling filter

46. Aeration tank of an activated sludge installation in a metropolitan sewage treatment plant

47. Inner workings of an activated sludge installation

48. A small-scale activated sludge operation used to process dairy waste