| With the rapid development of chemical, pharmaceutical, food processing and petroleum refining industries, the discharge of high strength and degradation-resistant organic wastewaters are increasing year by year. Sulfur and nitrogen laden organic wastewater is a typical case which has brought about a long-term and bad effects on organisms and environment. However, up to date, the prevailing problems of this wastewater treatment lie in insufficient applicability, complicated process system, great investment, high running cost, difficult up-to-standard discharge, and specially the prominent environmental risk of sulfide. An integrated reactor system was developed for the simultaneous removal of carbon, sulfur and nitrogen from sulfate-laden wastewater and for biological sulfur(Bio-S0) reclamation. It consists of 4 units:(a) sulfate reduction and organic carbon removal unit(SR-CR);(b) autotrophic and heterotrophic denitrifying sulfide removal unit(DSR),(c) sulfur reclamation unit(Bio- S0R),(d) aerobic nitrification(AN) unit. The technology can realize the simultaneous removal of highlevel organic carbon, sulfate, and ammonia. The sulfate is converted into sulfur, and the resourcezation of waste water is becoming possible using the technology.The effects of key operational parameters on production of elemental sulfur were investigated, including hydraulic retention time(HRT) of each unit, sulfide/nitrate(S2--S/NO3--N) ratios, reflux ratios between the DSR and AN units, and loading rates of chemical oxygen demand(COD), sulfate and ammonium. Physico-chemical characteristics of biosulfur were studied for acquiring efficient S0 recovery. The experiments successfully explored the optimum parameters for each unit and demonstrated 98% COD, 98% sulfate and 78% nitrogen removal efficiency. The optimum HRTs for SR-CR, DSR and AN were 12 h, 3 h and 3 h, respectively. The reflux ratio of 3 could provide adequate S2--S/ NO3--N ratio(approximately 1:1) to the DSR unit for obtaining maximum sulfur production. In this system, the maximum production of S0 reached 90%, but only 60% S0 was reclaimed from effluent. The S0 that adhered to the outer layer of granules was deposited in the bottom of the DSR unit. The effects of different COD/SO42- ratios on the performance of the integrated C-N-S removal system were investigated. This study provided insights into microbial community succession and the functional role of the dominant species in the SR-CR unit under various COD/SO42- ratios. When the COD/SO42- ratio was between 1:1 and 3:1, the SR-CR unit could find a balance between the sulfate-reducing efficiency and the methane-producing efficiency. The SR-CR unit could thereby provide appropriate concentrations of TOC and dissolved sulfide for the DSR unit to realize a maximum S0 conversion efficiency. When the COD/SO42- ratio was higher than 3.5:1 or lower than 1:1, the SR-CR unit was found to exhibit insufficient sulfate reduction efficiency. The performance of the DSR unit is greatly affected by insufficient sulfate reduction in the SR-CR unit. There was no significant effect of the lactate, molasses and starch as the carbon sources on the S0 conversion rate in this system. It can make the SR-CR unit produce appropriate concentration of sulfide and TOC for the DSR unit by increasing the HRT. The organic acids can be used by heterotrophic denitrifiers at optimum C/S/N ratios in the DSR unit.To better separate biological sulfur from denitrifying sulfide removal(DSR) unit, we determined a new method by research on the distribution characteristic of biological sulfur in this process system, Zeta potential, particle size distribution, scanning electron microscope and energy spectrum analysis. The results showed that biological sulfur in the effluent and sludge accounted for 65% and 35% of the total sulfur production, respectively. S content of biological sulfur particles is no less than 60%. The zeta potential value was approximately-19 m V, between ± 30 m V, indicating that the sulfur colloid was not stable. The sizes of most of the elemental sulfur particles were between 1 and 101 μm with a mean size of 27 μm. The above biological properties indicated that it have characteristics of colloid. The biological sulfur flocculation rate is approximately 99% when using cationic coagulant to separate biological sulfur. Coagulation is an effective method of separating biological sulfur form(DSR) process. The biosulfur flocculation on PAC, PAM and MBF was investigated in a batch system.The single and combined effects of operating parameters such as flocculant dose, p H and stirring intensity were analyzed using response surface methodology(RSM).Very high regression coefficient between the variables and the response indicates excellent evaluation of experimental data by second order polynomial regression model. The response surface method indicated that the optimum flocculation conditions were p H 4.63,129 rpm and 2.42 mg PAC/mg S. At optimum flocculation conditions, the bio-sulfur flocculation rate reached 96.47% actually. It can be obtained that PAC which has quite high bio-sulfur flocculation capacity can be utilized for the recovery of bio-sulfur.In the investigation of performance and control measures on the integrated C-N-S removal system for pharmaceutical wasterwater treatment, firstly, comparative study was made for start-up efficiency by raw wastewater, dilute wastewater using tap water and sewage.The influent of start-up was carried by dilute wastewater using sewage could shorten the start-up time and increased the tolerance of the system to toxicity and salinity gradually. Meanwhile, this method of start-up could increased the operation efficiency by 10%. To obtain stable operation for the system, we dealed with how to use methan production process to assist sulfate reduction removing excess carbon source in the SR-CR unit. p H and HRT could effectively control the relationship between two kinds of bacteria. Thus, when the TOC/NO3--N and S2--S/NO3--N was respectively between 3-4.5 and 0.8-1.5 in the DSR unit, the system would obtain maximum bio-S0 production rate. By adjusting the concentration of the influent, HRT and p H could a balance between sulfate-reducing and methane-producing efficiency of the SR-CR unit. The reflux ratios of 3:1 between A&H-DSR and AN units is still the key point for stable running of the system. When the system running at high loading rate, we determined the limited loading rate of 18.36 kg COD m-3 d-1(influent COD 8140mg/L). This system can achieved 95.34% COD, 95.34% ammonia nitrogen and 95% sulfate ramoval rate and its effluent can meet the discharge standard. Finally, the microbial community structure of the corresponding unit at different operational stage were analyzed by 16 S r RNA gene based high throughput Illumina Mi Seq sequencing and the potential function of dominant species were discussed. The heterotrophic and autotrophic denitrifiers in the DSR unit were well cultivated for producing bio-sulfur. Paracoccus, Ochrobactrum and Thauera strains likely acted as the heterotrophs to play a key role, whereas species from Thiobacillus and Melioribacteraceae strains are the autotrophs that required to generate a high-rate system.This study also provided insights into microbial community succession and the functional role of dominate species in the integrated system in response to different operational stages. After accounting for running cost, an average of 1 ton wastewater treatment produces 0.55 kg of bio-sulfur and take the cost of the PAC is 0.58 yuan, while the system can meet effluent standard and reduce running cost. |
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