Biological waste treatment

Figure 26. Process diagram for revised groundwater and solvent wastes biological treatment system.

J. W. Blackburn. 1989. Improved understanding and application of hazardous waste biological treatment processes using microbial systems analysis techniques. Hazard. Waste Hazard. Mat. 6(2) 173-193. 

Prepare the aqueous waste for biological treatment by removing excessive load or components that will inhibit the biological processes. 

The pretreatment processes may be most effective when applied to individual waste streams from particular processes or process steps before effluent streams are combined for biological treatment. 

The capital cost of most aqueous waste treatment operations is proportional to the total flow of wastewater, and the operating cost increases with decreasing concentration for a given mass of contaminant to be removed. Thus, if two streams require different treatment operations, it makes no sense to mix them and treat both streams in both treatment operations. This will increase both capital and operating costs. Rather, the streams should be segregated and treated separately in a distributed effluent treatment system. Indeed, effective primary treatment might mean that some streams do not need biological treatment at all. 

Z. Evaporation. If the wastewater is in low volume and the waste material involatile, then evaporation can be used to concentrate the waste. The relatively pure evaporated water might still require biological treatment after condensation. The concentrated waste can then be recycled or sent for further treatment or disposal. The cost of such operations can be prohibitively expensive unless the heat available in the evaporated water can be recovered. 

AH other organic waste-process and vent streams are burned in a dare, in an incinerator, or in a furnace where fuel value is recovered. Wastewater streams are handled in the plant biological treatment area. 

A comprehensive analytical program for characterising wastewaters should be based on relevance to unit treatment process operations, the poUutant or pollutants to be removed ia each, and effluent quality constraints. The qualitative and quantitative characteristics of waste streams to be treated not only serve as a basis for sising system processes within the facility, but also iadicate streams having refractory constituents, potential toxicants, or biostats. Such streams are not amenable to effective biological treatment, as iadicated by the characterization results, and requite treatment usiag alternative processes. 

Trickling Filters. The so-called trickling filter is not a filter but a bed of stones or other coarse material (packing) over which the sewage flows. In terms of the total number of installations, it is the most widely used biological treatment process. However, the greatest total volume of waste is treated by the activity-sludge process (12). 

There are two methods of biological treatment aerobic and anaerobic (217). The aerobic systems use free oxygen dissolved in the wastewater to convert wastes in the presence of microorganisms to more microorganisms, energy required for their existence, and carbon dioxide. The anaerobic process occurs in the absence of free oxygen and converts the waste to methane and carbon dioxide, generally in deep tanks or basins, and can produce odor problems when sulfides or sulfates are present in the wastewater. 

Three-phase fluidized bed reactors are used for the treatment of heavy petroleum fractions at 350 to 600°C (662 to 1,112°F) and 200 atm (2,940 psi). A biological treatment process (Dorr-Oliver Hy-Flo) employs a vertical column filled with sand on which bacderial growth takes place while waste liquid and air are charged. A large interfacial area for reaction is provided, about 33 cmVcm (84 inVirr), so that an 85 to 90 percent BOD removal in 15 min is claimed compared with 6 to 8 h in conventional units. 

One aspect of the basic equation describing biological treatment of waste that has not been referred to previously is that biomass appears on both sides of the equation. As was indicated above, the only reason that microorganisms function in waste-treatment systems is because it enables them to reproduce. Thus, the quantity of biomass in a waste-treatment system is higher after the treatment process than before it. 

A 3 Gaseous (gases, vapors, airborne particulates) W = Wastewater (aqueous waste) B11 Biological Treatment - Aerobic... 

L = Liquid waste (non-aqueous waste) B21 Biological Treatment - Anaerobic... 

S = Solid waste (including sludges and siurries) B31 Biological Treatment - Facultative... 

Typically, the biological treatment system operates best when a waste stream is at a pH near 7. However, waste treatment systems can operate (with some exceptions) between pH values of 4 and 10. The... 

Skladany, G.J., J.M. Thomas, G. Fisher and R. Ramachandran. The Design, Economics and Operation of a Biological Treatment System for Ketone Contaminated Ground and Solvent Recovery Process Waters. Presented at the 42nd Annual Purdue Industrial Waste Conference, Purdue University, West Lafayette, Indiana, 1987. 

Irvine, R.L., S.A. Sojka and J.F. Colaruotolo. Enhanced Biological Treatment of Leachates from Industrial Landfills. Hazardous Waste, Vol 1, No. l,1984.pp. 123-135. 

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