Study On N-Phenylglycinonitrile Wastewater Treated By Air Stripping-MAP-Two Phase Anaerobic Digestion Process

N-Phenylglycinonitrile was a kind of dye intermediate which would produce a large number of wastewater of high concentration of COD and ammonia nitrogen in its production process. The wastewater was a kind of low biodegradability chemical wastewater with complex component. In order to remove high concentration of ammonia nitrogen in wastewater for the latter biological treatment, we used air-stripping and MAP as the pretreatment. The wastewater after pretreatment was pumped into two-phase anaerobic digester to study the feature of TPAD process in dealing with startup and phase splitted, and the kinetics equation was obtained after reaction kinetics analysis studied. The feasibility of treatment by actived sludge after anaerobic treatement and variation of bacterial community were also studied.Concentration of Ammonia nitrogen in N-Phenylglycinonitrile wastewater was up to 7000mg/L¹2000mg/L,if the MAP applied directly it would consume a large quantities of chemicals which could lead to high consumption in unit treatment, and the effect was not good enough. So MAP applied after the air-stripping process was feasible that could reduce concentraion of ammoina nitrogen to 1500mg/L²000mg/L, and we could recovery tail gas. The best condition determined by the experiment was: air-stripping time=180min, temperature=70℃, gas-water ratio=2000:1, pH=11. Air-stripping would remove 5.8% COD, but the wastewater would get into darkness.Using MgO and H₃PO₄ as the MAP agent, the optimal operation parameters of MAP was determined by orthogonal experiment: magnesium oxide and ammonia nitrogen stoichiometric ratio=2.5:1, ammonia nitrogen and phosphate ratio=1:1.2, reaction pH=9.5. Under the condition above, there would be 100mg/L¹50mg/L NH₃-N and 15²0 mg/L phosphate remain in the wastewater. Experiments showed that the sediment was not easy to settle down for the reason that small particles of hyrophobic substances in wastewater attached to the sediments' surface, so that big particles of sediment was not easy to form for that they could not easily getting access from each other. But it would not occured after changing pre-prepared into paste precipitant dosage.Acclimated seed sludge was from coking plant in Chongqing Steel Group which feeded with orginal wastewater. Holding influent COD concentration 500mg/L, we did a duration of 12 days'facultative anaerobic acclimation and 10 days'adaptive anaerobic acclimation. After sludge suffered changing of substrates and living environment, the degradation strengthened gradually, and the remove rate of COD reached 50%. Acclimation run into load anaerobic acclimation after 22 days, and in low load stage (COD=500¹000mg/L) , TPAD remove over 60% COD, in medium load stage (COD=1000²000mg/L),the removal rate of COD was about 80%, in high load stage (COD>2000mg/L), removal rate was high as medium load stage at first, but it would drop down with the concentration increase, for the reason was the ammonia nitorgen concentration was up to 470 mg/L, and bacterias would get depressed. The ammonia nitrogen must be removed before wastewater pumped into TPAD.Putting a dosage of 2mol/L Na2MoO4 as methanogens inhibitor lasted for 3 days. In this process, effluent pH drop down from 8 to 7, and VFA rised from 400mg/L to 800mg/L, alkalinity(CaCO₃) dropped from 800mg/L to 400mg/L. During these days, COD removal rate dropped down for a while, but it ran into normal quickly.The TPAD reactor reached its highest condition when influent COD up to 7058 mg/L which was after ammonia nitrogen removing pretreatment. The COD removal rate was 55%, and the souring reactor could remove 11.1% COD, 1st methane reactor could remove 17.4% COD, 2st methane reactor could remove 25.1% COD. TPAD effluent was treated by actived sludge treatment to study the feasibility of aerobic treatment after diluting COD to 1000mg/L. When HRT was 16h, actived sludge treatment could remove 61.3% COD and 76.1% chroma.We got N-Phenylglycinonitrile biodegradation dynamic model with 1st methane reactor, 2st methane reactor and TPAD reactor by curve fitting with Origin software custom fitted curve based on Nerfeld modified Monod equation. Research on bacterial community by contrasting acclimated sludge with seed sludge in different treatment unit with PCR-TGGE technique, we draw conclusion as follows: acclimating process could change bacterial diversity and community greatly, the dice coefficient between seed sludge and acclimated sludge was 48.0%,48.2%,59.7%,56.8% and 50.6%,50.2%, Analysis of NMDS showed there were differences in sludge of first steps of souring process, but less difference in the last steps, and more less differences between 1st methane sluge and 2st methane sludge.