Enhanced Nitrogen And Phosphorus Removal Of Wastewater By Using Sludge Anaerobic Fermentation Liquid As Carbon Source

Studies have shown that the sludge anaerobic fermentation liquid could facilitate the removal of nitrogen and phosphorus in wastewater, but these experiments are mostly small scale experiments that treating synthesis wastewater. To further verify the actual feasibility of the project, the present study constructed an A2/O reactor system with a total effective volume of 4660 L and real municipal wastewater for treatment. Firstly investigated the possibility of enhanced nitrogen and phosphorus removal in wastewater using sludge anaerobic fermentation liquid as external carbon source; Then studied the factors and the optimum condition on recovering nitrogen and phosphorus from sludge fermentation liquid; Focused on various factors, such as temperature, recovery of nitrogen and phosphorus and adding dosage of acetic acid and sludge fermentation liquid,that influenced on nitrogen and phosphorus removal efficiency; And finally explored the mechanism of sludge fermentation liquid enhanced nitrogen and phosphorus removal. The main contents and conclusions:(1) Feasibility study on enhancing nutrient removal of wastewater by using sludge anaerobic fermentation liquidAt room temperature, under the conditions of the influent COD at 243.7 mg/L, NH4+-N at 30.9 mg/L, TN at 42.9 mg/L, TP at 2.8 mg/L, the backflow ratio of nitrification liquid at 200% and recycle ratio of sludge at 100%, the addition of acetic acid into anoxic tank can enhance the removal efficiency of nitrogen and phosphorus with the optimum influent quantity and SCOD incremental of carbon were 7500 L/d and 50 mg/L, respectively. When the sludge fermentation liquid was used as external carbon source and the average effluent COD, NH4+-N, TN, TP removal efficiency were 81.60%, 88.91%, 64.86% and 87.61%, the effluent concentrations were 42.18, 2.77, 11.92 and 0.19 mg/L, respectively. It can meet China’s first Class(A) criteria specified in the Discharge Standard Urban Sewage Treatment Plant Pollutant(GB18918-2002), and has the same strengthening effect on nitrogen and phosphorus removal with acid.(2) Recovery of nitrogen and phosphorus from fermentation liquid in the form of struviteThe optimum parameters of recovering nitrogen and phosphorus from sludge fermentation liquid in the form of struvite separately were Mg:P = 2.0, p H 11, stirring time 5 min; Under optimum conditions, soluble orthophosphate(SOP), TP and ammonia removal efficiency were 88.84%, 82.99% and 24.00%,respectively.(3) Study on factors of affecting enhanced nutrient removal by adding external carbon sourceUnder different climatic conditions, enhanced biological nutrient removal system by using sludge fermentation liquid had different treatment effect. Under normal temperature conditions, simply adding 50 mg/L of fermentation liquid could be able to obtain better treatment efficiency and a high operational stability, while at low temperature need to increase the dose of the fermentation liquid. Whether at low or normal temperature conditions, nitrogen and phosphorus removal efficiency would improve with the increase of acetic acid or fermentation liquid dosage, while increase carbon sources dosage due to a shortage of SCOD in sewage or low temperature, need to remove the nitrogen and phosphorus before adding, which can significantly improve the operational effectiveness of the system. At low temperature, adding fermentation liqiud which has been removed nitrogen and phosphorus by struvite recovery, when SCOD increments of 100 mg/L, it can achieve a similar denitrification effect with acetic acid. The acetic acid and fermentation liquid dosing position would affect the nitrogen and phosphorus removal efficiency, and adding position of fermentation liqiud was relatively critical; Adding acetic acid to the anoxic tank cast more conducive to phosphorus removal, and adding fermentation liquid to anoxic tank was able to simultaneously promote nitrification and denitrification and phosphorus removal, so anoxic pool is the recommended adding position.(4) Mechanism of sludge fermentation liquid enhanced nitrogen and phosphorus removalDenitrification experiments showed that nitrate concentration showed a declining trend, and has obvious stages. The first phase, denitrification rate increased with the increase of fermentation liquid concentration; The second phase, the nitrate concentration was reduced to slow; The third stage is the plateau, nitrate concentrations remained stable. In this experiment, nitrate removal efficiency increased with the increase of fermentation liquid concentration, while the SCOD increments were 25, 50 and 100 mg/L, the corresponding nitrate removal efficiency were 47.50%, 52.51%, 56.11% and 63.54%, respectively.