ИСТИНА

The total annual production of municipal solid wastes in Russia accounts for 37.5 mln. tons from which more than 96% are currently disposed of via landfilling. As a result of microbial activity within a landfill, compression and water flows, a leachate containing a wide variety of intermediate organic degradation products and inorganic (including metallic) contaminants is produced. This leachate (if not collected and treated) poses dangerous environmental and health risks due to its impact on surface and ground waters. The primary objective of this paper was to develop an efficient lab scale technology for removal of organic, heavy metals and nitrogenous pollutants. As a first step of treatment of landfill leachates (total COD – 1.43-3.81 g/l, total nitrogen 90-162 mg/l), a performance of laboratory UASB reactors (total working volume - 2.54-2.68 l) has been investigated. Under hydraulic retention times (HRT) of around 0.3 days, when the organic loading rates (OLR) were around 5 g COD/l/day, the total COD removal accounted for 81 % with the effluent concentrations close to anaerobic biodegradability limit (0.25 g COD/l) for mesophilic (30 oC) and sub-mesophilic (20 oC) regimes. The psychrophilic treatment (10 oC) conducted under the average HRT of 0.34 days and the average OLR of 4.22 g COD/l/day showed a total COD removal of 47% giving the effluents (0.75 g COD/l) more suitable for subsequent biological nitrogen removal. All 3 temperature regimes used for leachate treatment were quite efficient for elimination of heavy metals (Fe, Zn, Cu, Pb, Cd) by concomitant precipitation in the form of insoluble sulphides inside the sludge bed. As a second step for treatment of psychrophilic anaerobic effluents (total COD – 0.74 g/l, total nitrogen 63 mg/l), a performance of aerobic biofilter (working volume of 0.7l) functioning in alternating aerobic/anoxic regime with a whole working cycle of 1 h has been investigated. At 20 oC, when duration of aerobic and anoxic phases was 35 and 25 min, respectively, the average HRT was 0.88 days while the average OLR was 0.76 g COD/l/d. The total COD removal accounted for 73% with the total COD effluent concentrations slightly oscillating around 0.18 g COD/l. The efficiencies of nitrification and denitrification were 93 and 79% resulting in the total nitrogen concentrations in the effluents around 16 mg N/l. A decrease of working temperature of the biofilter till 10 oC required a increase of HRT and decrease of aeration phase. After optimisation of these parameters (duration of aerobic and anoxic phases of 25 and 35 min, respectively, HRT of 1.1 days), a performance of biofilter at 10 oC was comparable to that at 20 oC. Thus, the application of sequenced anaerobic-aerobic treatment of landfill leachates was quite efficient for elimination of biodegradable COD, heavy metals and nitrogen giving effluents approaching to the current standards for direct discharge of treated wastewater.