Decentralized Domestic Sewage Treatment By A Multi-stage Slow Speed Infiltration System In Rural Areas

In order to solve the problem of serious pollution of rural domestic sewage and high content of nitrogen,phosphorus and organic matter in grey water,it is necessary to develop an economical and effective rural domestic sewage decentralized treatment technology adapted to Chin's national conditions.Based on the principle and technology of land slow percolation system and Filter system,a multi-stage slow speed infiltration system and multi-media vertical subsurface flow constructed wetland were constructed by using self-made iron-based biocarriers.The effects of HRT,seasonal variation and thermal insulation measures in winter on the multi-stage slow speed infiltration system were investigated.The removal performance of nitrogen,phosphorus and organic matter in gray water was determined.The variation of pollutant concentration along the system and removal mechanism were studied.At the same time,the multi-media vertical subsurface flow constructed wetland was used to deeply treat the effluent of the multi-stage slow speed infiltration system,and the economic benefits of these two systems were analyzed,which provided technical support for the deep treatment of rural living grey water.The research conclusions are as follows:?1?Quartz sand and volcanic rocks with good adsorption properties for NH₄⁺-N,NO₃^--N and TP were selected through isothermal adsorption comparison test of several common fillers,and iron-based biocarriers capable of efficiently removing nitrogen and phosphorus were added.A multi-stage slow infiltration system and a multi-media vertical subsurface flow constructed wetland were constructed to deeply treat rural grey water by physical-biological-electrochemical coupling.?2?The multi-stage slow speed infiltration system was constructed and studied under the condition of NH₄⁺-N 25 mg/L,TP 4 mg/L and COD 250 mg/L for 190 days of continuous operation.When HRT was 2 days,the removal rates of NH₄⁺-N,TP and COD reached 81%-95%in summer and autumn?10-33??,and the NH₄⁺-N,TP and COD in the effluent could reach the Grade A standard of the 'Emission Standard for Pollutants in Urban Sewage Treatment Plants"?GB 18918-2002?;The normal operation of the system at low temperature in winter?-2-7??can be maintained by adding thermal insulation measures.?3?The multi-media vertical subsurface flow constructed wetland could deeply treat the effluent of multi-stage slow speed infiltration system.When HRT was 3 days,the removal rates of NO₃^--N,NH₄⁺-N,TP and COD were 97.9%,90.9%,91.0%and 80.2%respectively.The effluent water quality can reach the A emission limit of the"Beijing Municipal Water Pollutant Comprehensive Emission Standard"?DB 11/307-2013?.?4?The investment cost per unit of sewage treatment volume of multi-stage slow speed infiltration system and multi-media vertical subsurface flow constructed wetland was 966 yuan/m³ and 839.5 yuan/m³,respectively.And the operating cost per unit sewage treatment volume was 0.202 yuan/m³ and 0.352 yuan/m³,respectively.The combined process proposed in this paper can be used in rural decentralized wastewater treatment economically and efficiently.44 sets of figures,16 tables and 129 references were included in this paper.