Study On Treatment Of Rural Non-point Source Wastewater With High-rate Algal Pond(HRAP)

Rural area non-point pollution, also known as rural non-point source pollution, means the pollutants generated when people are engaged in agricultural production and livelihood activities, including the pollution caused by agricultural runoff (fertilizers or pesticides loss), soil erosion, rural domestic wastewater, rural solid waste and livestock breeding. Currently, the annual emission load of rural domestic sewage is approximately 8 billion tons and it is increasing steadily in China, while the treatment of them is not optimistic without drainage and sewage treatment systems and in 96 percent of the villages, bringing about severe rural environmental contamination. Therefore, searching for treatment processes and operation mode for rural sewage to study rural sewage treatment technologies is of urgently practical significance.To research the rural non-point source domestic sewage against the status quo of rural non-point source pollution, a pilot apparatus for high rate algal pond (HRAP) was used to treat the artificial rural non-point source domestic sewage (referred to as sewage) and the optimum operational conditions, impact factors and reaction mechanism were systematically investigated during the process. The following valuable experimental results on treating livestock wastewater were given:(1) the maximum removal rate of NH4+-N, TP and CODCr were beyond 95%,80% and 92% respectively in the HRAP under the optimal operational conditions of full aeration, temperature 24-35℃, light intensity 4000 Lux, pH 7.5 and algae concentration 8× 105/mL, based on Knop medium as the best medium for algae. (2) The effects of trace metals on removal efficiency of NH4+-N, TP and CODcr in HRAP were optimized by Box-Behnken design based on response surface methodology. When the iron (Fe3+), manganese (Mn2+) and magnesium (Mg2+) concentration were 1 mg/L,0.5 mg/L and 0.5 mg/L respectively, the actual removal rates of NH4+-N, TP and CODCr were 93.62%,85.62% and 96.02%, respectively, in accord with the predicted value of 94%,86.4% and 97.00%. (3) The results for the treatment of actual livestock wastewater in Algae pond indicated that algal concentration had significant effect on NH4+-N, TP removal efficiency, but had little effect on COD removal efficiency. (4) Four kinds of bacteria for nitrogen and phosphorus removal were screened from the algae pond with the basal medium. The effects of single and mixed species on NH^-N, TP and COD removal efficiency were also investigated and the results revealed that bacteria C had the maximum nitrogen and phosphorus removal capacity. Three strains named A, C and D with larger nitrogen and phosphorus removal capacity were chosen to be primarily identified and determined as Chryseobacterium massiliae, Micrococcus luteus strain and bacteria Stenotrophomonas maltophilia strain, respectively. (5) The mechanism of the removal of NH4+-N, TP and COD under these four strains with different concentrations of K+ and Na+ was analyzed, it was found that the concentration of Na+ had little effect on the removal efficiency of NH4+-N, TP, COD in strains, but it significantly affected the NH4-N, TP, COD removal efficiency with excess or insufficient K+, which revealed that the cell membrane permeability can be adjusted with K+ to boost the absorption of pollutants.