[Research on sludge toxicity caused by DMF biodegradation and toxicity spatial distribution in sludge flocs].

The aerobic sequencing batch activated sludge system (SBR) was used to remove the toxic and refractory organic pollutant, N,N-dimethylformamide (DMF). The formation property and spatial distribution of the organic toxicity in sludge were studied. The operation parameters were controlled as follows: influent COD was about 300 mg x L(-1), every DMF concentration phase lasted 30 d(40 mg x L(-1), 80 mg x L(-1), 120 mg x L(-1)), the SBR cycle lasted 12 h, and DO was 2.0-3.0 mg x L(-1). The results showed that the sludge toxicity increased in the beginning and then decreased to a steady range at each DMF concentration phase; there was a positive correlation between the sludge toxicity and the initial DMF concentration; most of the sludge organic toxicity was caused by DMF biodegradation and existed in the inner extracellular polymeric substances (EPS) and intracellular section of sludge flocs.

[Effective nitrogen removal in low C/N wastewater with combined aerobic-low DO biofilm treatment process].

The municipal wastewater in China is characterized by low ratio of carbon to nitrogen, which is the key restrictive factor for effective biological removal of nitrogen. In this study, the aerobic-low DO biofilm process was used for the nitrogen removal of municipal wastewater. By means of adjusting inflow ratios of aerobic section to low-DO section, hydraulic retention time (HRT) and inflow ratio of carbon to nitrogen (C/N), the performances of nitrification in aerobic biofilm section and denitrification in low-DO section could be improved, the good performance of nitrogen removal was achieved. In order to insure the good effluent quality, especially for ammonia nitrogen and total nitrogen indexes, the nitrification and denitrification could be made up in aerobic and low-DO biofilm section respectively due to the coexistence of aerobic and anoxic zone in biofilm. There were 3 stages for the research process. In the first stage, the original C/N, inflow ratios of aerobic section to low-DO section were chosen as 3:1 and 1:1 respectively, then the effects of various HRT (aerobic section + low DO section) values such as (10 + 5) h, (8 + 4) h, (6 + 3) h, (4 + 2) h to nitrogen removal were analyzed. According to the conclusion in the first stage, the original C/N was kept at 3:1, HRT (aerobic section + low DO section) was (10 + 5) h. Then, the effects of various inflow ratios to nitrogen removal were studied in the second stage. In the third stage, when HRT(aerobic section + low DO section) was (10 + 5) h and inflow ratio was 1:1, the original C/N were adjusted from 2:1, 3:1, 5:1 to 10:1. To conclude, the optimal parameters for nitrogen removal in the biofilm system were as follows: original C/N = 5:1, inflow ratio of aerobic to low-DO section = 1:1, HRT of aerobic and low-DO sections were 10 h and 5 h respectively. As a result, COD, ammonia nitrogen and total nitrogen could be removed from 254 mg/L to 48 mg/L, 37.2 mg/L to 9.3 mg/L and 48.2 mg/L to 14.8 mg/L respectively.