Biological treatment of wastewaters from pesticide and starch manufacture

Treatment processes were developed for two different industrial wastewaters, both with a high GOD. Both processes involved aerobic treatment and removed substantial quantities of pollutants. The similarity ends there, as the microbial populations and the results differed in almost every possible way. The pesticide wastewater had a high COD and contained a variety of pesticides, mainly endosulphan 1 and 2, diazinon, malathion, atrazine, simazine, chlorpyrifos and others in a total concentration of c. 1.6 g/L. Normal disposal methodology involves encapsulation and costs several thousands of dollars per cubic meter. The bench-scale research described in this paper involved ozonation, biological granulated activated carbon treatment, biofilter treatment only and chemical coagulation with microfiltration. A process without activated carbon was studied in parallel. Both the biofilter and biological activated carbon with coagulation and separation with microfiltation were able to remove about 99% of most pesticides, with the bulk of the removal occurring during the biological treatment stage. A notable exception was simazine, which left persistent residues. While ozonation improved the COD removal, it was not deemed an essential treatment component. The effluent would have been suitable for sewer discharge with costs two orders of magnitude less than encapsulation. The starch wastewater had a COD of 12300 mg/L (of which 7900 mg/L soluble), a BOD of c. 9600 mg/L, a TOC of 4550 mg/L and presented a disposal problem mainly as high sewer discharge fees to the manufacturer. A single, nonaseptic fungal treatment process was developed, which not only removed 95% of the BOD and 78 to 85% of the total organic carbon (TOC), but produced a biomass product with a protein content of 38 to 48%, suitable for animal feeds. Different strains of Aspergillus oryzae and Rhizopus arrhizus were found to be suitable, but the efficiency of conversion of waste to fungi was substantially influenced by the species and strain of organism selected. The yield achievable was 1.3 to 1.44 g biomass/g TOC. Addition of plant nutrients was not essential, but some increase in biomass production could be achieved with phosphate, magnesium and calcium supplementation. An air lift reactor configuration was developed with air spargers and external recirculation resulting in velocity gradients which favored the growth of pelletized colonies. These are easily harvested and dewatered by screening. Further dewatering could be done with a simple process such. as belt pressing.