Feasibility Of Agriculture Land Disposal Of Sewage Treated In Different Levels

Great efforts have been devoted in many cases to treat rural domestic sewage to reach up to meat the discharging standards.However,diversity of complex process technologies and high cost in maintenance have resulted in the difficulty to achieve this goal.Granted that effluent of treatment satisfied the standard,potential contamination risks still exist for the receiving water.Futhermore,considering that rural domestic sewage hardly contains any heavy metals or toxic substances but rich in nitrogen and phosphorus resources,employing soil-plant system of agricultural land to dispose these sewage would be reasonable in long-term perspective.Although,agricultural irrigation of sewage is a traditional ritual in China,change of sewage componants caused by improvement of residents’ life quality deserves our attention to studying on the impact of rural sewage irrigation on crops and soil environment and exploring feasibility of agriculture land disposal of sewage treated in different levels.Three types of sewage were collected from different tanks of treatment device including raw water,anaerobically treated water and effluent from AO system,representing three different treating levels.These three types of sewage were set as experimental subjects to irrigated three agricultural lands(three treated groups).As a comparison,control was irrigated with clean water.Lab and field experiments were both carried out to explore influence of these sewage irrigation on the crop and soil properties to explore feasibility of agriculture land disposal of sewage.The main results can be listed as following:(1)From the perspective of crop quality,in the laboratory experiments,water spinach biomass of three treated groups was significantly higher by 25.59%～38.28%compared with controlling one.Among these three treated groups,raw water irrigation yielded the maximum production,but coming with the maximum risks of quality decline.In this very group,nitrate and nitrite concentration within the water spinach was significantly higher than control,whereas the vitamin C content was significantly lower.Similar conclusion was drew in the field experiment.In the filed experiments,production of radish and corn in the three treated groups was significantly higher by 49.01%～50.67%and 16.48%～21.69%,respectively,compared with their component,control.Further studies pointed out that anaerobically treated water irrigation group yielded the maximum production,while not posing significant side effect on radish and corn quality.(2)From the perspective of soil quality,influence of the sewage irrigation on soil quality was negligible as the content of organic matter,nitrogen,phosphorus and potassium in the soil was not found significantly different among four experimental groups.Similar situation happened to the enzyme activity.(3)In the lab experiment,driven by absorption and transformation capability of plant-soil system,pollutants in the sewage declined significantly after penetrating the soil columns.Therefore,agricultural land featured a great capability to absorb pollutants in the rural domestic sewage.(4)Dominant phyla or genera were quite similar among the groups.In detailed,there were 16 genera varying greatly among the groups in the lab experiment,in contract to 3 genera in the field experiment,suggesting that fully opened agricultural land may possess a more stable and better buffering capacity for the pollutants shock.(5)Among aforementioned 16 genera,6 genera were soil beneficial bacteria,4 genera were endophytic bacteria(Solirubrobacter,Mesorhizobium,Bradyrhizobium,Variovorax),1 genus was slime bacteria(Haliangium),1 genus was biocontrol bacteria(Lysobacter).More specifically,relative abundance of Bradyrhizobium,Variovorax and Haliangium were found significantly higher in anaerobic reclaimed water irrigation group.And relative abundance of Haliangium followed the same rule in both lab and field experiments.So,irrigation of agriculture land with the anaerobic reclaimed water would facilitate the beneficial bacteria in the soil.It could be concluded that it would be relatively reasonable to dispose anaerobically treated water with agricultral land concerning about its positive effect on the crops’production and growth of soil beneficial microorganisms and minimum negative effect on crops’ quality and soil properties.Hence,the study has provided the practical basis for the rational utilization of the rural domestic sewage.