Study Of The Combination Of UASB+A/O+BAF Treating Organic Wastewater With High Concentration Ammonia-nitrogen

Microorganism were used to produce AM in a chemical plant, and high consistence of CODcr and NH3-N were caused in the produce wastewater. The combination of UASB+A/O+BAF was used to dispose the wastewater. Anaerobic granular sludge was cultivated and acclimated by favorable technological conditions. And most organic matter was removed by granular sludge because of its high specific methanogenic activity. A/O process was used to remove NH3-N. NC3- and NO2-were reduced to N2 by denitrification which reduced organic matter as carbon source at the same time. The consistence of CODcr was low in the effluent,and it was favorable for the reproduction of nitrobacteria. NH3-N was oxidized to NC3- and NO2-by nitrobacteria and was removed by refluxed to anoxic zone. The surplus CODcr and NH3-N were removed by BAF process,and the effluent reached secondary standard of the national sewage effluent discharge standards (GB8978-1996).This paper analysed the forming condition of anaerobic granular sludge and the principle of nitrogen remove by animalcule. The start of UASB process and A/O process and BAF process and operation condition were also studied in this paper.(1) The appearance of anaerobic granular sludge was the symbol of successful start of UASB process. The influent was intermittent when the UASB started, and the organic load was 1.0kgCODcr/(m3·d).The raise of CODcr and NH3-N load was step by step until the design load. When the system run steady, the organic load was 3.2kgCODcr/(m3.d) and the NH3-N load was 0.2 kgNH3-N/(m3·d). The partical size of granular sludge was 0.5 to 2 mm until 100days.(2) The CODcr consistence of influent was 3500 to 5000mg/L, and the average was 4000mg/L, and the effluent CODcr consistence was 1000 to 1200mg/L.The remove rate was 75% to 80%, and the UASB had the ability to resist shock load. The NH3-N consistence of influent was 150 to 400mg/L, and the average was 250mg/L, and the effluent NH3-N consistence was about 280 mg/L and the ammoniation rate was 15%.(3) A large number of VFA was produced in the process of anaerobic metabolism and caused pH reduction and the ammoniation of organic nitrogen produced basicity which was to buffer pH.The influent pH was controlled at 6.5 to 8 and basicity was more than 1000mg/L(in the form of CaCO3) in UASB process in order to prevent acidification.(4) The influent was intermittent too when the A/O started. The organic load was 0.5kgCODcr/(m3·d), and NH3-N load was 0.15kgNH3-N/(m3·d). NH3-N load was raised to enrich nitrobacterium after microorganism adapted to wastewater. The generation cycle of nitrobacterium was long and were enriched by controlling the CODcr consistence and increasing the NH3-N load and extending the sludge age. The remove rate of NH3-N reached 80% until 80days and A/O was successful started. When it run steady, the organic load reached 1.5kgCODcr/(m3·d) and NH3-N load reached 0.4kgNH3-N/(m3·d).(5) The experiments and practice showed that the best operation condition were: the internal recycle ratio was 200%, and the sludge reflux ratio was 100%. The temperature was 25 to 35℃, and the pH was 7.0～8.0 in oxic zone and was 6.8 to 7.5 in anoxic zone. The DO was 2 to 3mg/L at the inlet and was 3 to 5mg/L at the outlet and was 0.5 to 0.8mg/L in anoxic zone. MLSS was controlled at 2500 to 3500mg/L and SV30 was 25 to 30%.(6) The organic load and nitrogen load were raised with A/O process at the same time in BAF process. The remove rate of CODcr and NH3-N were 50% and 60%, and biofilm colonization was completed until 30days. The practice showed that the remove rate of CODcr and NH3-N were high when the gas-water ratio was 3 to 4 and DO was 2 to 3mg/L(7) Back wash was an important parameter for BAF. The combination of gas-water was used in back wash. The remove rate can return to normal when gas-wash flow rate was controlled at 1.2m3/(m2.min) and water-wash flow rate was controlled at 0.4m3/(m.min) and the pulse duration of air blast was controlled at 3 to 5min and gas-water wash time was controlled at 5 to 8min and water—wash time was controlled at about 5min.(8) When the system run steady, the effluent CODcr was 50 to 150mg/L and NH3-N was 10 to 25mg/L. And remove rate of CODcr and NH3-N were 60% to 65% and 70% to 75%.(9) The total remove rate of CODcr reached 97% and NH3-N reached 96.7% by the compositional process, and various index accorded with the regulation of secondary standard of the national sewage effluent discharge standards (GB8978-1996).