Kun Li

Microwave-acid pretreatment: A potential process for enhancing sludge dewaterability.

Activated sludge is hard to be dewatered due to the highly water bounded in sludge flocs. This study investigated the hybrid treatment of microwave irradiation and acidification on sludge dewaterability as well as its mechanism. Results showed that the combined microwave-acid treatment (Txa0=xa0100xa0°C, initial pHxa0=xa02.5) was effective for improving sludge dewaterability, e.g. capillary suction time (CST) decreased from 37.7xa0s to 9.2xa0s, bound water content decreased from 1.96xa0±xa00.19xa0g/g Dry Sludge (DS) to 0.88xa0±xa00.24xa0g/g DS. The treated sludge showed more fluidity and less thixotropy. Both MW heating temperature and pH played important roles in improving sludge dewaterability. Higher temperature was beneficial for sludge disintegration, but the released polymers resulted in highly negative zeta potential and deteriorated sludge dewaterability. The acidification was capable of reducing the negative zeta potential, increasing flocs size and finally improving sludge dewaterability. According to the analysis of molecule weight distribution and 3D-EEM, the fractions of polymers especially protein-like substances at molecule weight of 10(4)-10(5)xa0Da were the key organics related to sludge dewaterability, but not the humic acid-like and fulvic acid-like substances.

Performance and fate of organics in a pilot MBR–NF for treating antibiotic production wastewater with recycling NF concentrate

A double membrane system comprising a membrane bioreactor (MBR) combined with a nanofiltration (NF) membrane was investigated on a pilot scale for the treatment of antibiotic production wastewater over a three-month period at a pharmaceutical company in Wuxi, China. By recycling the NF concentrate, the combined MBR-NF process was shown to be effective for the treatment of antibiotic production wastewater, resulting in excellent water quality and a high water yield of 92±5.6%. The water quality of the pilot-scale MBR-NF process was excellent; e.g., the concentrations of TOC, NH4(+)-N, TP were stable at 5.52, 0.68, 0.34 mg L(-1), respectively, and the values of turbidity and conductivity of the NF permeate were 0.15 NTU and 2.5 mS cm(-1), respectively; these values meet Chinas water quality standard requirements for industrial use (GB21903-2008). Not only were the antibiotic removal rates of spiramycin (SPM) and new spiramycin (NSPM) over 95%, the acute toxicity was also drastically reduced by the MBR-NF pilot system. The main organics in the MBR effluent were proteins, polysaccharides, and humic-like substances; they were almost completely retained by the NF membrane and further biodegraded in the MBR because the NF concentrate was recycled. The microbial community of the MBR did not significantly change with the recycling of the NF concentrate.

Influence of natural zeolite and nitrification inhibitor on organics degradation and nitrogen transformation during sludge composting

Sludge composting is one of the most widely used treatments for sewage sludge resource utilization. Natural zeolite and nitrification inhibitor (NI) are widely used during composting and land application for nitrogen conservation, respectively. Three composting reactors (A—the control, B—natural zeolite addition, and C—3,4-dimethylpyrazole phosphate (DMPP) addition) were established to investigate the influence of NI and natural zeolite addition on organics degradation and nitrogen transformation during sludge composting conducted at the lab scale. The results showed that, in comparison with the control, natural zeolite addition accelerated organics degradation and the maturity of sludge compost was higher, while the DMPP addition slowed down the degradation of organic matters. Meanwhile, the nitrogen transformation functional genes including those responses for nitrification (amoA and nxrA) and denitrification (narG, nirS, nirK, and nosZ) were quantified through quantitative PCR (qPCR) to investigate the effects of natural zeolites and DMPP addition on nitrogen transformation. Although no significant difference in the abundance of nitrogen transformation functional genes was observed between treatments, addition of both natural zeolite and DMPP increases the final total nitrogen content by 48.6 % and 23.1 %, respectively. The ability of natural zeolite for nitrogen conservation was due to the absorption of NH3 by compost, and nitrogen conservation by DMPP was achieved by the source reduction of denitrification. Besides, it was assumed that the addition of natural zeolite and DMPP may affect the activity of these genes instead of the abundance.

Advanced treatment of municipal wastewater by nanofiltration： Operational optimization and membrane fouling analysis

Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration (NF) in this study. The NF performance was optimized, and its fouling characteristics after different operational durations (i.e., 48 and 169hr) were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure=12bar, pH=4 and flow rate=8L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6hr which is 175% longer than that of the 48-hr one. High molecular weight (MW) protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.

Fate of organic pollutants in a pilot-scale membrane bioreactor-nanofiltration membrane system at high water yield in antibiotic wastewater treatment

A double membrane system combining a membrane bioreactor (MBR) with a nanofiltration (NF) membrane at the pilot scale was tested to treat real antibiotic wastewater at a pharmaceutical company in Wuxi (China). The water yield of the pilot system reached over 92 ± 5.6% through recycling the NF concentrate to the MBR tank. Results showed that the pilot scale system operated in good conditions throughout the entire experiment period and obtained excellent water quality in which the concentrations of chemical oxygen demand and total organic carbon were stable at 35 and 5.7 mg/L, respectively. The antibiotic removal rates of both spiramycin (SPM) and new spiramycin in wastewater were over 95%. Organics analysis results showed that the main organics in the biological effluent were proteins, soluble microbial by-product-like, fulvic acid-like and humic-like substances. These organics could be perfectly rejected by the NF membrane. Most of the organics could be removed through recycling NF concentrate to the MBR tank and only a small part was discharged with NF concentrate and permeate.

Fouling analysis of membrane bioreactor treating antibiotic production wastewater at different hydraulic retention times

Membrane fouling, including foulants and factors, was investigated during hydraulic retention time (HRT) optimization of a membrane bioreactor (MBR) that treated wastewater from the production of antibiotics. The results showed that HRT played an important role in membrane fouling. Trans-membrane pressure (TMP), membrane flux, and resistance were stable at −6xa0kPa, 76xa0Lxa0m−2xa0h−1xa0bar−1, and 4.5u2009×u20091012xa0m−1 when HRT was at 60, 48, and 36xa0h, respectively. Using Fourier transform infrared spectroscopy, foulants were identified as carbohydrates and proteins, which correlated with effluent organic matter and effluent chemical oxygen demand (COD) compounds. Therefore, membrane fouling trends would benefit from low supernatant COD (378xa0mgxa0L−1) and a low membrane removal rate (26xa0%) at a HRT of 36xa0h. Serious membrane fouling at 72 and 24xa0h was related to soluble microbial products and extracellular polymeric substances in mixed liquor, respectively. Based on the TMP decrease and flux recovery after physical and chemical cleaning, irremovable fouling aggravation was related to extracellular polymeric substances’ increase and soluble microbial products’ decrease. According to changes in the specific oxygen uptake rate (SOUR) and mixed liquor suspended solids (MLSSs) during HRT optimization in this study, antibiotic production wastewater largely inhibited MLSS growth, which only increased from 4.5 to 5.0xa0gxa0L−1 when HRT was decreased from 72 to 24xa0h, but did not limit sludge activity. The results of a principal component analysis highlighted both proteins and carbohydrates in extracellular polymeric substances as the primary foulants. Membrane fouling associated with the first principal component was positively related to extracellular polymeric substances and negatively related to soluble microbial products. Principal component 2 was primarily related to proteins in the influent. Additional membrane fouling factors included biomass characteristics, operational conditions, and feed characteristics.

The color removal and fate of organic pollutants in a pilot-scale MBR-NF combined process treating textile wastewater with high water recovery

A combination of membrane bioreactor (MBR) and nanofiltration (NF) was tested at pilot-scale treating textile wastewater from the wastewater treatment station of a textile mill in Wuqing District of Tianjin (China). The MBR-NF process showed a much better treatment efficiency on the removal of the chemical oxygen demand, total organic carbon, color and turbidity in comparison with the conventional processes. The water recovery rate was enhanced to over 90% through the recycling of NF concentrate to the MBR, while the MBR-NF showed a stable permeate water quality that met with standards and could be directly discharged or further reused. The recycled NF concentrate caused an accumulation of refractory compounds in the MBR, which significantly influenced the treatment efficiency of the MBR. However, the sludge characteristics showed that the activated sludge activity was not obviously inhibited. The results of fluorescence spectra and molecular weight distribution indicated that those recalcitrant pollutants were mostly protein-like substances and a small amount of humic acid-like substances (650-6,000 Da), which contributed to membrane fouling of NF. Although the penetrated protein-like substances caused the residual color in NF permeate, the MBR-NF process was suitable for the advanced treatment and reclamation of textile wastewater under high water yield.

Interconnected PVDF-CTFE hydrophobic membranes for MD desalination: effect of PEGs on phase inversion process

In this work, poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) was used for hydrophobic membrane preparation by the non-solvent induced phase inversion (NIPS) technique. The effects of poly(ethylene glycol) (PEG) molecular weight and dosage were investigated in terms of the membrane morphology, contact angle, surface free energy, and membrane pore structure for both surface pores and overall pores. All membranes possessed a typical liquid–liquid demixing asymmetric structure and the contact angles were higher than 85°. Furthermore, increasing the PEG molecular weight and dosage significantly altered the membrane pore structure and surface roughness as a result of the variation of the phase inversion process. The solid–liquid demixing was responsible for the variation of membrane morphology, pore structure, hydrophobicity, and DCMD performance as PEGs with higher molecular weight or dosage were added. The PVDF-CTFE membranes were suitable for MD application owing to their high hydrophobicity, small pore size with narrow pore distribution, high DCMD performance, especially the interconnected pore structure. The membrane containing 5 wt% PEG-400 was evidenced to be the optimal one for the MD process, mainly according to the high interconnected pore structure which provide more passages for vapour transfer. The permeate flux was 17.98 kg (m−2 h−1) with a conductivity as low as 7 μS cm−1 at the temperature difference of 30 °C. In addition, an excellent performance sustainability was observed including a relatively steady permeate flux and conductivity during the 360 h continuous DCMD operation.

Fouling characteristics and cleaning strategies of NF membranes for the advanced treatment of antibiotic production wastewater

The nanofiltration (NF) membrane fouling characteristics and cleaning strategies were investigated through a laboratory-scale NF fouling test treating membrane bioreactor (MBR) effluent and MBR-granular activated carbon (GAC) effluent of an antibiotic production wastewater by DK and NF90 membranes, respectively. Results showed that organic fouling is the main NF membrane fouling for treating both the MBR effluent and MBR-GAC effluent. Soluble microbial by-product (SMP)-like and aromatic protein-like substances were the dominant components in the foulants, whereas humic-like substances had little contribution to the NF fouling. The fouling of DK was more severe than that of NF90. However, foulants respond by UV254 were more easily to foul NF90 membrane. It could get satisfactory effect using combined cleaning of acid (HCl, pHxa02.0∼2.5) and alkali (NaOHu2009+u20090.3xa0wt% NaDS, pHxa010.0∼10.5). The favorable cleaning strategy is “acidu2009+u2009alkali” for treating MBR-GAC effluent, while it is “alkaliu2009+u2009acid” for treating MBR effluent.

Comparison of NF membrane fouling and cleaning by two pretreatment strategies for the advanced treatment of antibiotic production wastewater

The nanofiltration (NF) membrane fouling characteristics and cleaning strategies were investigated and compared for treating membrane bioreactor (MBR) effluent and MBR-granular activated carbon (GAC) effluent of an antibiotic production wastewater by DK membrane. Results showed that the fouling of treating MBR effluent was more severe than that of treating MBR-GAC effluent. After filtering for 216 h, the difference of membrane flux decline was obvious between MBR effluent and MBR-GAC effluent, with 14.9% and 10.3% flux decline, respectively. Further study showed that organic fouling is the main NF membrane fouling in the advanced treatment of antibiotic production wastewater for both of the two different effluents. Soluble microbial by-product like and tyrosine-like substances were the dominant components in the foulants, whereas humic-like substances existing in the effluents had little contribution to the NF membrane fouling. A satisfactory efficiency of NF chemical cleaning could be obtained using combination of acid (HCl, pH 2.0-2.5) and alkali (NaOH + 0.3 wt% NaDS, pH 10.0-10.5). The favorable cleaning strategy is acid-alkali for treating the MBR-GAC effluent, while it is alkali-acid for treating the MBR effluent.