[Sodium hypochlorite disinfection on effluent of MBR in municipal wastewater treatment process].

Sodium hypochlorite (NaClO) used in wastewater disinfection was assessed by examining its performances in lab fed by the effluent from a MBR treatment plant. The influence of sodium hypochlorite initial concentrations (0.5-3.0 mg/L) on the presence of indicator microorganisms (total coliforms, fecal coliforms), disinfection by-products (DBPs) concentrations and the acute toxicity were evaluated. Results indicate the total coliforms and the fecal coliform were 1500-2400 and 10-40 CFU/L, which is difficult to meet the present reclaimed water quality standards. A chlorine dose of 2.0 mg/L and contact for 1 h could achieve a 3 lg indicator bacteria reduction in MBR effluent samples. THMs (trihalomethanes) analysis indicated that concentrations of THMs increase with the raise of the active chlorine dose. After adding sodium hypochlorite 1 h the concentrations of trihalomethanes (THMs) were 16.22, 7.35 microg/L respectively and chloroform (TCM) accounted for 87% of THMs, the haloacetic acids (HAAs) was involved trichloroacetic acid (TCAA) 2.01 microg/L, dichloroacetic acid (DCAA) 1.58 microg/L and under the national limits. Luminescence bacteria acute toxicity analysis showed that the chlorinated effluent has higher inhibition rate (48%) in comparison to the control with a chlorine dosage of 3.0 mg/L. The results which could provide theoretical basis to production show that NaClO disinfection not only can inactivate microbe with the DBPs and acute toxicity of the effluent under the safety limits, but also meet the requirement of health and safety.

[Research on the organic biodegradability of secondary effluent treated by ozonation].

The secondary effluent of three WWTPs was treated by ozonation to investigate organic biodegradability enhancement. The bulk experimental method was used. Ozone adding dosage was controlled to be 2, 4, 6, 8, 10 mg/L by adjusting the adding time. Results showed, UV254 and SUVA(UV254/DOC)decreased with the increasing of the ozone dosage. When ozone adding dosage was 6 mg/L, UV254 and SUVA decreased about 54.4% and 56.6% respectively; while BOD5/COD, BDOC and BDOC/DOC were improved above 30%, 360% and 360% respectively. It could be concluded that suitable ozonation could improve the biodegradation of the organic substances in the secondary effluent. The organic substance was analyzed by the excitation-emission matrix (EEM) to investigate the variation regularity of organic matter changes of the ozoned and non-ozoned secondary effluent. The main organic substances of the secondary effluent in the plant were aromatic protein like substances and humic substances, ozone could significantly remove these types of organic substance.

[Application of GFH in the municipal effluent reuse for landscape].

In order to prevent increased algae growth for the reuse of reclaimed water as landscape water, the removal mechanism of phosphate, DOM and nitrogen by adsorption onto GFH was studied. The result showed that the removal rate of phosphate was the highest, when the influent concentration of TP was 0.059-0.725 mg/L, and the concentration of PO4(3-) -P was 0.004-0.684 mg/L, the effluent concentration of TP was less than 0.05 mg/L(removal rate was 91.1%), and of PO4(3-) -P was less than 0.023 mg/L(removal rate was 95.4%) by adsorption onto GFH. GFH could remove macromolecular DOM (mainly fulvic acids) preferentially, and removal rate of DOM was 28.5%, but which would improve the aromaticity proportion of DOM. Because of the strong oxidizing property of GFH and O3, NH4(+) -N and NO2(-) -N occurred nitrification in reclaimed water, the average removal rates of NH4(+) -N and NO2(-) -N were 37.3% and 59% respectively.

[Autotrophic nitrogen removal and enhanced biological phosphorus removal from municipal wastewater in a three-sludge system].

Using a three-sludge system consisted of anaerobic/oxic (A/O) process, partial nitritation and anaerobic ammonium oxidation (ANAMMOX) reactors, cost-effective removal of nitrogen and phosphate from municipal wastewater was achieved. The experimental results showed that effluent total phosphorus (TP) of the A/O system was less than 0.5 mg/L under hydraulic retention time (HRT) of 3.6 h. Partial nitritation with nitrite accumulation efficiency of 75% -96% was realized in the partial nitritation system under room temperature, DO < 0.2 mg/L and HRT of 4.6 h. Under temperature of 27-30 degrees C and HRT of 1.4 h, effluent total nitrogen (TN) and TN removal rate of ANAMMOX reactor were less than 8 mg/L with the minimum value of 1.6 mg/L and 0.57 kg/(m3 x d), respectively. In the three-sludge system, phosphate accumulating organisms, ammonia-oxidizing bacteria and Anammox bacteria existed under suitably environmental condition to optimize the microbial community structure and improve treatment efficiency of various units. Autotrophic nitrogen removal can reduce 62.5% of the oxygen supply, save 100% of denitrification carbon sources theoretically, lower the sludge production, and greatly decrease carbon dioxide emission. As compared to traditional biological nutrient removal process, the three-sludge system has great advantages and potential in energy saving and carbon dioxide emission reduction to realize sustainable development of water resources.

[Partial nitrification of digested sludge liquor with low C/N and high-concentration ammonia].

The experimental system consisted of anoxic filter and aerobic suspended carrier biofilm reactor. The partial nitrification was achieved and maintained stably in the aerobic reactor under normal temperature (15-29 degrees C) and high DO (6-9 mg/L). The nitritation with 70%-80% nitrite accumulation efficiency was obtained when FA concentration was in the range of 1.0-10.3 mg/L by controlling influent ammonia loading rate (ALR), ratio of alkalinity and ammonia and HRT in the aerobic reactor. The effluent nitrite/ammonia ratio was about 1.25 when the average influent ammonia, influent ALR and influent ratio of alkalinity and ammonia were 315.80 mg/L, 0.43 kg/(m3 x d) and 5.25, respectively. So the effluent of partial nitrification process provided the influent substrate demand for the following ANAMMOX process. The integrative analysis indicated that the proper FA concentration was the main factor achieving the partial nitrification. The study developed a novel partial nitrification technology adapt to water characteristics of digested sludge liquor.

[Half-nitrosofication of dewatering liquid of digested sludge with high ammonia].

The affecting factors and controlling methods of how realizing and maintaining half-nitrosofication of dewatering liquid of digested sludge were investigated in an A/O process. The experimental results showed that the nitritation was obtained in 29 d under bulk liquid temperature of 9-20 degrees C, average DO of 5.4 mg/L, SRT of about 30 d and influent ammonia loading rate of 0.64 kg/(m3 x d). The nitritation with 70% nitrite accumulation efficiency was maintained during 65 d when average FA concentration in A/O reactor was more than 4 mg/L. Furthermore, the half-nitrosofication with effluent ammonia and nitrite ratio of 1:1.32 was obtained. When the ammonia loading rate reduced to 0.19 kg/(m3 x d) (FA < 1 mg/L), the nitritation disappeared, and the high FA as a main factor of maintaining half-nitrosofication was proved again with FISH under the condition of different FA. TN removal concentration was about 91 mg/L under influent COD of 282 mg/L and raw C/N ratio of 0.85 in the A/O system, which due to nitritation saving much carbon sources. The study showed that the half-nitrosofication of the dewatering liquid was obtained and stably maintained when FA was more than 4 mg/L in the A/O reactor by dynamic controlling influent ammonia loading rate and pH value in the system under middle or low temperature, high DO, long SRT.

[Start up and maintain of nitritation by the inhibition of FA and FNA].

In order to treat the digested sludge dewatering liquor bypass and reduce influent ALR of wastewater treatment plant, the startup and maintenance of nitritation was investigated in an A/O reactor. NOB activity was inhibited and nitritation was stated up successfully by increasing the influent ALR (in N, the same below) step by step from 0.23 kg/(m3 x d) to 0.78 kg/(m3 x d), in spite of normal temperature, long SRT and high DO concentration. Due to the deficiency of alkalinity in influent, nitritation could be maintained steadily by the associated inhibition of free ammonia (FA) and free nitrous acid (FNA). The nitrite accumulation ratio always kept at above 90% during the period of maintaining nitritation for 30 days, and correspondingly the average concentration of DO was higher than 2 mg/L. The nitrite accumulation ratio did not decline even if the average DO concentration increased to 4.8 mg/L, which demonstrated that high DO could not destroy the nitritation built by the associated inhibition of FA and FNA. The concentration of FNA at the last chambers was increased by reducing the influent ALR in order to enhance the inhibition of FNA. The nitritation was still maintained for two months although the inhibition of FA was weakened. But the nitritation was destroyed completely in 3 days after the inhibition of FNA was eliminated, which showed the inhibition of FNA to NOB was very critical to maintain steadily nitritation.