ИСТИНА

Baker’s yeast industry is abundant in Russia: such factories exist in almost all Russian provinces and altogether they produced 56 mln. m3 wastewater per year. These wastewaters are high strength (10-80 g COD/l), strong nitrogenous (0.5-1.5 g/l total N), sulphate-rich (2-10 g/l), phosphorous variable (sometimes P-deficient), recalcitrant for biodegradation and highly coloured (melanoids etc) ones. Currently many yeast factories are faced with heavy trade-effluent charges. Land disposal options generate problems with ground water pollution and are prohibited in majority of the Russian regions. Many local municipal sewage treatment plants are now insisting on pre-treatment of such effluents before discharge into their sewerage. The objective of this paper was to develop a laboratory technology for treatment of baker’s yeast wastewater to meet the limits for discharge of treated wastewater into municipal sewerage. The most troublesome limits in this case are the following (mg/l, except colour): COD – 800; SO42- - 500; total N – 100; N-NH3 – 50; P-PO43- - 3.5; colour threshold 1:128). As a first treatment step, the UASB reactor operating at 35 oC was applied for the elimination of the major part of COD and concomitant sulphate reduction. In a subsequent step, the biofilter operating in alternative aerobic-anoxic regime at ~20 oC was used for the removal of remaining BOD and nitrogen. Finally, coagulation with Fe, Al & Ca was tested to fulfil the limits on COD, total nitrogen, PO43- and colour. From the results obtained during such a comprehensive study, the following conclusions can be drawn. The UASB reactor was quite efficient for removal of bulk COD (60-70% efficiency) even for such high strength wastewater as from yeast separation process. The aerobic-anoxic biofilter can be used for removal of remaining BOD and ammonia from anaerobic effluents; however, it suffered from COD-deficiency to fulfil denitrification requirements. To balance COD/N ratio, some bypass of raw wastewater should be added to the biofilter feed. The application of coagulation for post-treatment of aerobic effluents may fulfil the discharge limits (even for colour exerted by hardly biodegradable melanoids), however, the required amount of inorganic coagulants were relatively high.