Study On Nitrogen Conversion And Reuse Of High Strength Domestic Wastewater Based On BF-MBR Process

In the closed-loop regenerative system named Controlled Ecological Life Support System?CELSS?,the goal of domestic wastewater treatment is to complete the recycling of water and nutrient elements?such as nitrogen?in wastewater with minimal cost and supply of substances.Theory and practical experience show that the improved biological treatment technology was the best choice for domestic wastewater treatment in the CELSS.However,due to the low dilution ratio,the domestic wastewater in CELSS haver higher concentration of detergent and urine,and its organic load and nitrogen load were much higher than that of conventional domestic sewage.This greatly increases the difficulty of biological treatment,and it was easy to cause incomplete nitrification and accumulation of nitrite,leading to a decrease in the recovery rate of nitrogen and affecting the growth of plants and the health of personnel of CELSS.Meanwhile,there are several issues that should be considered to improve the biological treatment process,incuding reducing the production of excess sludge,reducing the consumption of solid-liquid separation membrane modules,reducing the alkalinity replenishment for nitrification.So,it is necessary to optimize the wastewater treatment process to improve the efficiency of nitrogen nitrification,ensuring the recycling of effluent,and reducing the material consumption.This paper have designed and constructed an two-stage?anaerobic and aerobic?BF-MBR process to treatment the domestic wastewater?including sanitary wastewater and urine wastewater?in CELSS to meet the water quality requirements for recycling as plant nutrient solution.The affect of p H,HRT and urine strength,on organic matter removal and nitrogen conversion efficiency were studied,two sets of optimal process operating parameters were obtained:?1?1/5 urine strength,HRT 2 d,p H 6.4?6.5,which was applicable when the treated effluent was used as the sole or main source of plant nutrient solution;?2?1/10 concentration urine,HRT 1 d,p H 6.4?6.5,which was applicable when the treated effluent was used as supplement of plant nutrient solution.The developed system could treat the 1/5 concentration urine wastewater at the highest level.At this time,TOC removal ratio was 94.3%,the nitrification efficiency of the system was 90.6%.Under the condition of 1/10 concentration urine and HRT0.5 d,the system obtained the highest ammonia oxidation capacity of 0.774 kg N?m³·d?^-1,and under the condition that the HRT was 1 d,the system obtains the highest nitrous oxide oxidation capacity of 0.418 kg N?m³·d?^-1.Which proved that the nitrification capacity of the constructed system in this paper was higher than conventional biological treatment system.The short-term action mechanism and kinetic parameters of nitrification process in different p H and ammonia nitrogen concentration system were discussed.And the most suitable conditions for the expression of AOB and NOB activity were obtained,they were the initial concentration 50 mg L^-1of ammonia nitrogen and the p H 6.6±0.1 respectively.At this time,the maximum specific growth rate of ammonia oxidizing bacteria reached 1.203 d^-1,and the maximum specific growth rate of nitrite oxidizing bacteria reached 0.48 d^-1.The plant cultivation experiments experiment was carried out by using the treated wastewater as the main source of plant nutrients to explore the feasibility and reuse mode of the treated wastewater as the plant nutrient solution.The comparative analysis of plant growth status and plant yield showed that the reuse wastewater could meet the growth needs of two types of crops,mesembryanthemum cordifolium L.F and celery,after supplementing phosphorus and micronutrient elements.And plants could effectively use the mineral elements in the reuse wastewater.The mesembryanthemum cordifolium L.F cultivated by the reuse wastewater showed the best growth state and plant yield,and the sodium salt absorption capacity of the cordifolium was verified,which was expected to provide a new way for the extraction and recovery of sodium chloride in the CELSS.The constructed two-stage BF-MBR process in this paper could effectively achieve the organic matter removal and nitrogen conversion of the domestic wastewater in CELSS,and the effluent could be directly used as plant nutrient solution for plant cultivation.Which will provide a useful reference for the design of the biological treatment system of domestic wastewater and the plant cultivation system in CELSS.