Waste water Purification of town Kushevskaya, Krasnodar region is done on the Combined installations and works (CW). Sewage first comes to the inlet chamber of the sewage treatment facilities, flows to the step-like fine mechanical purification grids, then goes to vertical sand catchers and finally arrives in CW mixing chamber, composed of 4 sections. Each section consists of flat-feed boifilter and aerotank. In the mixing chamber sewage mixes with circulating sludge mud, fed from aerotank. After that sewage goes directly to the sprinking system of biofilter. Next, liquid goes to aeration columns where water-jet air entrainment occurs. With the help of water-air mixture oxygenation and sludge mud mixing in the aerotank aeration zone occurs. Purified water from sedimentation zones goes directly to collecting trays and then it is discharged first to disinfection zones and finally to bio basins.
Technological scheme of sewage purification is shown in the picture 1.

While waste water treatment installations projecting the information on impurities content was received from Kushevskaya village authorities. The level of impurities according to this data was equal to average residential sewage level. Commissioning works started in December 2008 and base values at that period were as follows: chemical oxygen demand mgО/dm³–up to 400; biological oxygen demand for 5 days-mgО/dm³ up to 200; suspended materials mg/dm³, up to 180; phosphates (РО₄³), mg/dm³-up to 6; ammonium ions, mg/dm³ up to 25,0; sulfides+ hydrogen sulfides, mg/dm³–up to 5. In January 2009 water treatment installation was put in operation. Degree of purification met projected indexes within chemical oxygen demand and biological oxygen demand for 5 days (30 mgО/dm³ и 15 mgО₂/dm³ respectively). Remaining sulfides and hydrogen sulfides content in aerotank was 0,014 mg/dm³. In the beginning of March qualitative characteristics of incoming water have changed dramatically: chemical oxygen demand mgО/dm³–up to 1400; biological oxygen demand for 5 days-mgО/dm³ up to 720; suspended materials mg/dm³, up to 309; phosphates (РО₄³), mg/dm³-up to 21; ammonium ions, mg/dm³ up to 84; sulfides+hydrogen sulfides, mg/dm³–up to 42,1. Initial waste water was sludgy, of grey color. Intensive hydrogen sulfide smell could be felt, that is most probably due to special manner of small settlements channeling. Thus, for example, Kushevskaya village is channeled for only 60%. In this case residential sewage flows to septic tanks and later sewage cesspool tank trucks take it to waste water treatment stations. Moreover 800 farm enterprises are located in Kushevskaya village and its’ sewage also flows to septic tanks, where organic substances biotransformation occurs and high concentration of hydrogen sulfide, ammonia and phosphates is discharged to waste liquid. In spring during the water table rise septic flooding began and the decision was taken to deliver waste water to waste water treatment stations.
Another reason of not typically high level of Н₂S in residential sewage was infiltration hydrogen sulfide containing ground waters. It should be noted that the characterization of wastewater may vary widely even within one day.
When concentration of reduced sulfur compounds was increasing, activate sludge inflation in CW aerotank sediment zone was noted. Provided that purified water indexes exceeded admissible limit value. The necessity of sewage delivery to waste water treatment station with the help of sewage cesspool tank trucks was approved. However, the concentration of impurities in sewage remained higher than admissible limit value. In addition, it should be noted that the characterization of sewage changed greatly within one day. In consequence adaptation of activated sludge to the appropriate wastewater occured. Over the next 10 months waste water treatment facility exploitation with high initial concentrations of reduced sulfur compounds it was found that CW constructive characteristics enable effective cleaning within chemical oxygen demand and biological oxygen demand for 5 days indexes. It happened due to reducing the negative impact of hydrogen sulfide and sulfides on the oxidation of organic contaminants. This result is achieved by the absence of primary sedimentation tanks in the technological scheme, which leads to the cessation of sulfate reduction in the initial stage of purification. In the irrigation system and the plane loaded biofilter with a film liquid flow on the surface there is a transition of hydrogen sulfide into the atmosphere according to its partial pressure. In addition the process sorption and oxidation of sulfides immobilized microflora takes place in biofilter, which lowers the burden of sulfides on aeratank activated sludge. Water jet aeration system used in CW, enables flexible management of dissolved oxygen concentration in the interstitial fluid of aeration tank. Moreover higher utilization of atmospheric oxygen in comparison with other aeration systems is noted in CW aeration system. As shown by the process of exploitation, the use of CW permits to achieve high-quality treatment for all indicators when initial content of reduced sulfur compounds is up to 14 mg/dm³, which is the undoubted advantage of CW in comparison with classical aeration tanks. When the concentration of hydrogen sulfide is over 14 mg/dm³ it is strongly recommended to use two-step purification scheme based on the CW’s advantages plus using of reagent-oxidants. Pic. 2 presents the technological scheme, elaborated for deep residential and industrial sewage purification. The content of organic contaminants in these type of sewage within biological oxygen demand for 5 days is from 100 to 1,500 mgO₂/dm³, suspended solids from 100 to 700 mg/dm³, the total content of hydrogen sulfide and hydrosulfides to 40 mg/dm³, and ammonia nitrogen up to 100 mg/dm³.

After being mechanically processed with the help of grids and sand catchers, the sewage is discharged into mixing chamber of the 1st stage where it mixes with 30-35% hydrogen peroxide solution . Entering the reagent provides oxidation of hydrogen sulfide and sulfur colloid to hydrosulfides and sulfates and reduces their inhibitory effect on biocaenosis. In addition, according to the research, the concentration of dissolved oxygen in the wastewater increases to 5-6 mg/dm³, which intensifies the process of biological treatment. Introduction of hydrogen peroxide in the mixing chamber of CW of the first stage is useful when the concentration of reduced sulfur compounds is over 20 mg/dm³, or when the concentration of reduced sulfur compounds is more than 8 mg/dm³ and the concentration of organic substances within biological oxygen demand for 5 days is mgO₂/dm³. Dose of hydrogen peroxide-10-100 mg/dm³-is determined empirically, taking into account the initial concentration of reduced sulfur compounds and. Degassing of hydrogen sulfide, biodegradation of organic pollutants within biological oxygen demand for 5 days by 50-70% and the process of partial denitrification (10-15%) take place in biofilter. Length of sewage stay in aeration zone of CW of the first stage is 1-3 hours. This stage is primarily intended for reducing the concentration of organic matter, reduced sulfur compounds and the assimilation of ammonium nitrogen. To reduce the load of organic matter on the first stage CW biocaenosis within concentration of organic substances in wastewater on BOD₅ more than 500 mg/dm³, partial sludge supply from 2nd stage CW into the mixing chamber of the 1st stage CW is foreseen. Next wastewater is directed into CW 2nd stage mixing chamber, where at low loads of sludge organic matter (0,05-0,1 kg BOD per 1 kg of ashless substance), the process of complete oxidation of organic impurities and deep processes of nitrification and partial denitrification of nitrogen-containing compounds occurs. Period of sewage stay is 4-7 hours.This is also the place where sluge from the 1st sage is divected for mineralization. The proposed technological scheme will provide effective sewage treatment for villages and small towns with a significant length of gravity and pressure reservoir, when sewage contents of sulfide and hydrogen sulfide is up to 40 mg/dm³, this of ammonium nitrogen–up to 100 mg/dm³, that were generated as a result of decay processes of organic contaminants in collectors and receiving tanks pumping stations, and the delivery of sewage from septic tanks and cesspools.