Sewage treatment works (capacity 500 m3/day)
Scheme of domestic wastewater treatment
Sewage treatment works consists of the following: - the first option:
-Sewage pumping station (SPS);
-Block of main structures (BMS) with capacity of 500 m3/day;
-Sludge platforms or storage tank.
Block of main structures includes:
-Combined works (CW), consisting of: biofilters, aerotanks and mixing chamber with circulating pumps;
-Post-treatment bioreactors;
-Ultraviolet disinfection installation.
First wastewater enters SPS, from where it is pumped into CW mixing chamber. To capture the waste and sand sand catcher is installed into the mixing chamber. Captured waste and sand are loaded into the waste tank. In the mixing chamber sewage mixes with the circulating sludge mixture from aerotank. The mixture is then fed into biofilter irrigation system with the help of circulating pump. Irrigation system consists of water-distributing trays with discharge pipes and reflective discs. Falling liquid jets break up on discs and irrigate the biofilter loading. Sorption and oxidation of 60-70% of organic contaminants takes place in biofilter. Liquid, having passed through the biofilter, is sent to aeration columns, where air entrainment takes place (0,6 m3/m3) because of vortex funnels appearing. Air-water mixture is distributed by aeration columns over the volume of the aeration basin. Oxidation of the remaining impurities (30-40%) takes place in aerotank. Sludge mixture displaced from the aeration zone enters the zone of sedimentation, where it is split. Part of the sludge is compacted and through the slot returns to the zone of aeration. Another part of the sludge rises and forms a suspended layer for capturing the fine particles of impurities. Purified water is collected by drainage trays and directed by gravity into bioreactor with loading for post-treatment. Regeneration of bioreactors loading is done periodically by alternate evacuation and loading tanks flushing with water. Mud from bioreactors is directed into the mixing chamber. Purified water from bioreactors comes to UV disinfection installation.
Excess activated sludge is dumped to sludge platforms (if the sanitary protection zone exists-150 m).
The size of the sanitary protection zone can be reduced up to 50 m. But in this case, the BMS is equipped with used air decontamination and sludge dewatering installations.
Exceed sludge is mechanically dewatered in bag dryers. Dewatered exceed sludge (80% of moisture) is transported to the dump or after the process of deworming it is used as fertilizer. Supplementation with emergency sludge platforms of closed types performed as reinforced concrete tanks with air processing function is foreseen.
Justification of the proposed technology
1. For the construction of sewage treatment plants we propose a technology that has undergone all stages of testing and is recommended by GOSSTROY of RUSSIA (protocol No. 9 dtd 28.06.1989; Letter from Ministry of Construction of Russia No. BE-23-184/28 dtd 11.03.1997).
2. Reliability of technological mode of structures. At intervals in CW functioning, rapid restoration of active microflora in the aeration basin occurs due to the long-term vitality preservation in biofilter (two days and more). In existing aeration facilities while stoppage of work for more than 3 hours active microflora restoring takes 2- 3 weeks.
3. With BOS supplementation with air decontamination installation the size of sanitary protection zone can be reduced to 50 m.
4. Reliable technological mode allows reducing the number of staff up to 2 people.
5. Reduction of energy consumption. Power consumed by treatment facilities with pneumatic aeration system is 15 kWh. Power consumption of the proposed buildings is 6 kWh
6. CW implementation in enclosed design as well as high index of atmospheric oxygen utilization, due to repeated circulation of air through the biofilter and aerotank (amount of outside cold air on the biochemical processes reduces by 4-5 times), provides preservation and even increasing of treated water temperatures at 0,5-1oC, whereas in the aeration basins of extended aeration it falls in winter at 4-9oC that leads to the cessation of biochemical processes.