Protoplast fusion between Saccharomyces cerevisiae and Rhodobacter sphaeroides for the treatment of soybean wastewater

The kinetic parameters and the purification rates of the hybrid cell Foaz in soybean processing wastewater (SPW) were measured through a shaking reaction and in two automatic regulated control stable fermentation systems (ARCSFS). The maximum specific growth rate of Foaz was 0.576 h^‐1, higher than that of one of its parental strains Rhodobacter sphaeroides P9479 and lower than that of another parental strain Saccharomyces cerevisiae Y9407. The BOD₅ removal rate of Foaz in the No. 1 system was 61.3%, higher than those of both its parental strains when the influent BOD₅ concentration was 4600 mg/L. The results of this study suggest that the hybrid Foaz has a better capacity of the degradation of organic pollutants in SPW than its parental strains and it may be applicable to the treatment of high concentration organic wastewater.     

Acidogenic sludge fermentation to recover soluble organics as the carbon source for denitrification in wastewater treatment: Comparison of sludge types

For biological nitrogen (N) removal from wastewater, a sufficient organic carbon source is requested for denitrification. However, the organic carbon/nitrogen ratio in municipal wastewater is becoming lower in recent years, which increases the demand for the addition of external organic carbon, e.g. methanol, in wastewater treatment. The volatile fatty acids (VFAs) produced by acidogenic fermentation of sewage sludge can be an attractive alternative for methanol. Chemically enhanced primary sedimentation (CEPS) is an effective process that applies chemical coagulants to enhance the removal of organic pollutants and phosphorus from wastewater by sedimentation. In terms of the chemical and biological characteristics, the CEPS sludge is considerably different from the conventional primary and secondary sludge. In the present study, FeCl₃ and PACl (polyaluminum chloride) were used as the coagulants for CEPS treatment of raw sewage. The derived CEPS sludge (Fe-sludge and Al-sludge) was then processed with mesophilic acidogenic fermentation to hydrolyse the solid organics and produce VFAs for organic carbon recovery, and the sludge acidogenesis efficiency was compared with that of the conventional primary sludge and secondary sludge. The results showed that the Fe-sludge exhibited the highest hydrolysis and acidogenesis efficiency, while the Al-sludge and secondary sludge had lower hydrolysis efficiency than that of primary sludge. Utilizing the Fe-sludge fermentation liquid as the carbon source for denitrification, more than 99% of nitrate removal was achieved in the main-stream wastewater treatment without any external carbon addition, instead of 35% obtained from the conventional process of primary sedimentation followed by the oxic/anoxic (O/A) treatment.

Open image in new window

     

Coupled electrocoagulation–electro-Fenton for efficient domestic wastewater treatment

This article reports the first use of coupled electrocoagulation and electro-Fenton (EF-EC) to clean domestic wastewater. Domestic wastewater contains high amounts of organic, inorganic and microbial pollutants that cannot be usually treated in a single step. Here, to produce an effluent suitable for discharge in a single process step, a hybrid process combining electrocoagulation and electro-Fenton was simultaneously used to decrease chemical oxygen demand (COD), turbidity and total suspended solids (TSS) from domestic wastewater. The electrocoagulation–electro-Fenton process was firstly tested for the production of H₂O₂ using Ti–IrO₂ and vitreous carbon- or graphite electrodes arranged at the anode and the cathode, respectively. The concentration of H₂O₂ recorded at 1.5 A of current intensity during 60 min of electrolysis using vitreous carbon- and graphite electrodes at the cathode was 4.18 and 1.62 mg L^?1, respectively. By comparison, when the iron electrode was used at the anode, 2.05 and 1.06 mg L^?1 of H₂O₂ were recorded using vitreous carbon and graphite, respectively. The H₂O₂ concentration decrease was attributed to hydroxyl radical formation generated by the Fenton reaction. Electro-Fenton using iron electrode at the anode and vitreous carbon at the cathode with a current density imposed of 0.34 A dm^?2 ensures the removal efficiency of 50.1 % COD_T, 70.8 % TSS and 90.4 % turbidity. The electrocoagulation–electro-Fenton technique is therefore a promising secondary treatment to simultaneously remove organic, inorganic and microbial pollutants from domestic, municipal and industrial wastewaters.     

Pilot-scale studies of domestic wastewater treatment by typical constructed wetlands and their greenhouse gas emissions

Three typical constructed wetlands (CWs) including Vertical Flow (VF), Free Water Surface (FWS), and Subsurface Flow (SF), and combined VF-SF-FWS constructed wetlands were investigated for the treatment of domestic wastewater with low C/N ratio. The performance of nutrient removal and the characteristics of greenhouse gas emissions, such as CH₄ and N₂O, from these CWs were compared. The results indicated that the four types of CWs had high removal efficiencies for organic matter and suspended solid (SS). The combined wetland also showed a comparatively good performance for nitrogen and phosphorus removal, and the removal efficiencies for total nitrogen (TN) and total phosphorus (TP) were 81.3% and 84.5%, respectively. The combined CWs had a comparative lower global warming potential. The FWS CW had the highest tendency to emit CH₄ and led to a higher global warming potential among the four types of CWs, which was about 586 mg CO₂/m²·h.     

Strengthening effects of ammonia nitrogen on the harmless biological treatment of oily sludge

To improve the efficiency of oil degradation and strengthen the harmless treatment of oily sludge, three dominant strains identified as Chryseomicrobium sp. YL2, Gordonia sp. YL3 and Acinetobacter sp. YL5 were isolated from soil near a refinery, and the effects on the bioremediation of the oily sludge from the refinery were investigated. The results showed that the efficiency of oil degradation increased by 31.5% compared with the control when the dominant strains were added to the treatment of oily sludge. Furthermore, the dominant strains could use oil as a carbon source for heterotrophic nitrification–aerobic denitrification. The addition of ammonia nitrogen resulted in a large number of remaining microbes and heightened dehydrogenase activity in the oily sludge, further accelerating oil degradation, mainly for C₁₁ to C₂₅ saturated hydrocarbons, and the oil degradation efficiency increased by 40.8%. After 120 days of bioremediation, the biotoxicity of oily sludge, which was expressed by the equivalent phenol concentration, decreased by 40.0% compared with that of the control, indicating that the addition of ammonia nitrogen enhanced the biodegradation of oil. This method can be used to strengthen the harmless treatment of oily sludge in practical engineering applications.     

Heterogeneous Fenton oxidation of dissolved organics in salt-laden wastewater from leather industry without sludge production

This is the first report on the heterogeneous oxidation of dissolved organics in wastewater with little consumption of Fenton’s reagent and without sludge production. The salt-laden wastewater discharged from leather industry has poor biodegradability due to the presence of high total dissolved solids. This wastewater is evaporated in solar evaporation pans. The evaporated residue faces disposal problem due to high concentration of organic and inorganic salts. The present study demonstrates the preparation, characterization and application of mesoporous activated carbon matrix along with Fenton’s reagent for the removal of dissolved organics in wastewater. Free electron-rich mesoporous activated carbon matrices (MAC₇₀₀, MAC₈₀₀ and MAC₉₀₀) were prepared and characterized for surface area, C, H, N, ash content, free electron density and energy gap value. Results show that heterogeneous catalytic oxidation of dissolved organics in the wastewater decreased biochemical oxygen demand, chemical oxygen demand, total organic carbon and dissolved protein, respectively, by 74, 69, 61 and 80% at optimum pH (3.5), H₂O₂ (7.5 mmol/l), FeSO₄.7H₂O (0.3 mmol/l) and MAC₈₀₀ (10 g/l).     

N2O emission from a sequencing batch reactor for biological N and P removal from wastewater

Nitrous oxide （N2O） is a greenhouse gas that can be released during biological nitrogen removal from wastewater. N2O emission from a sequencing batch reactor （SBR） for biological nitrogen and phosphorus removal from wastewater was investigated, and the aims were to examine which process, nitrification or denitrification, would contribute more to N2Oemission and to study the effects of heterotrophic activities on N2O emission during nitrification. The results showed that N2O emission was mainly attributed to nitrification rather than to denitrification. N2O emission during denitrification mainly occurred with stored organic carbon as the electron donor. During nitrification, NaO emission was increased with increasing initial ammonium or nitrite concentrations. The ratio of N2O emission to the removed ammonium nitrogen （N2O- N/NH4-N） was 2.5% in the SBR system with high heterotrophic activities, while this ratio was in the range from 0.14% to 1.06% in batch nitrification experiments with limited heterotrophic activities.     

Algal purification of pretreated landfill Leachate

The efficiency of microalgae in removing various pollutants in landfill leachate after pretreatment by free stripping or air stripping was tested by a laboratory batch system. The results showed that Chlorella pyrenoidosa and Scenedesmus sp. had similar removal efficiencies with regard to ammoniacal‐nitrogen, oxidized‐nitrogen, orthophosphate and chemical oxygen demand (COD). The COD removal by algal treatment was better in Junk Bay (JB) leachate than in Gin Drinkers’ Bay (GDB) leachate (14–21% and 0.4–7% respectively). No significant difference (P > 0.05) was found in removing other nutrients including ammoniacal‐nitrogen, oxidized‐nitrogen and orthophosphate between leachate from the two landfills, regardless of the pretreatment used. The removal efficiencies of ammoniacal‐nitrogen and phosphorus were found to be higher in air‐stripped leachate than in free‐stripped one. Removal of ammoniacal‐nitrogen and phosphorus in air‐stripped leachate was 30% and 87% respectively. Poor removal of ammoniacal‐nitrogen was probably due to a deficiency in phosphorus (high N : P ratio) for algal growth in leachate. The two‐stage leachate treatment (ammonia stripping followed by algal purification) resulted in overall reduction of COD (38–51%), ammoniacal‐nitrogen (72–96%) and orthophosphate (79–96%).     

Photoelectrochemical treatment of ammonium using seawater as a natural supporting electrolyte

In the present study, a photoelectrochemical process containing seawater as a natural low-cost supporting electrolyte was used to remove ammonium from wastewater in a continuous flow mode. Based on central composite design (CCD), response surface methodology (RSM) was employed to evaluate the performance of the process in ammonia removal. The effect of four main independent parameters, including initial ammonium concentration, hydraulic retention time (HRT), current intensity and initial pH on the removal of ammonia was evaluated by the model. The optimal initial ammonium concentration, HRT, current intensity and initial pH were 917 mg NH ₄? N;·L ^?1, 108 min, 1.8 A and 8.4, respectively. The high coefficients (R ²=0.97 and adjusted R ²=0.94) obtained by the analysis of variance (ANOVA) demonstrated close correlation between predicted and experimental values. Also, treating the reject water from the sludge dewatering unit as an ammonium-rich wastewater showed the effectiveness of the process for treating real wastewaters (86% ammonium removal). The results revealed that the present process can be an efficient method for ammonium removal from polluted effluents in coastal areas based on the availability of seawater as a cost-efficient supporting electrolyte.     

Effects of metal pollution in the monosodium glutamate production effluent on full exploitation and biological treatment

Monosodium glutamate (MSG) effluent was sampled from three MSG mills and 21 metal elements were measured with a inductively coupled plasma (ICP) Spectrometer. The total metal concentration of each MSG wastewater sample was 19192, 3190 and 3161 mg/L respectively. Compared with the water quality standard issued by the Chinese Government and the World Health Organization (WHO), some values were found to exceed the standards. The 24hr‐LC₅₀, 48hr‐LC₅₀, 72hr‐LC₅₀ and 96hr‐LC₅₀ to the fish Ctenopharyngodon idellus were 6.9%, 3.2%, 2.5% and 1.4% MSG wastewater individually. The specific growth rate for photosynthetic bacteria (PSB) Rhodopseudomonas sphaeroides was inhibited by the metals in MSG wastewater. Therefor the MSG wastewater should not be discharged into drinking, irrigation and fishery water systems, moreover it cannot be treated by general biological processes efficiently. How to develop an effective biotechnique for the utilization of organic pollutants in MSG effluent will also be discussed in this paper.     

Effect of short-term atrazine addition on the performance of an anaerobic/anoxic/oxic process

In this study, an anaerobic/anoxic/oxic (A²O) wastewater treatment process was implemented to treat domestic wastewater with short-term atrazine addition. The results provided an evaluation on the effects of an accidental pollution on the operation of a wastewater treatment plant (WWTP) in relation to Chemical Oxygen Demand (COD) and biological nutrient removal. Domestic wastewater with atrazine addition in 3 continuous days was treated when steady biological nutrient removal was achieved in the A²O process. The concentrations of atrazine were 15, 10, and 5 mg·L^?1 on days 1, 2 and 3, respectively. The results showed that atrazine addition did not affect the removal of COD. The specific NH₄ ⁺ oxidation rate and NO₃ ^? reduction rate decreased slightly due to the short-term atrazine addition. However, it did not affect the nitrogen removal due to the high nitrification and denitrification capacity of the system. Total nitrogen (TN) removal was steady, and more than 70% was removed during the period studied. The phosphorus removal rate was not affected by the short-term addition of atrazine under the applied experimental conditions. However, more poly-hydroxy-alkanoate (PHA) was generated and utilized during atrazine addition. The results of the oxygen uptake rate (OUR) showed that the respiration of nitrifiers decreased significantly, while the activity of carbon utilizers had no obvious change with the atrazine addition. Atrazine was not removed with the A²O process, even via absorption by the activated sludge in the process of the short-term addition of atrazine.     

Application of electrochemical reactor divided by cellulosic membrane for optimized simultaneous removal of phenols,chromium, and ammonia from tannery effluents

The post treatment of simulated tannery wastewater was evaluated in an electrochemical oxidation process under galvanostatic conditions. A continuous flow reactor divided by a cellulosic membrane consisted of Ti/SnO₂–Sb anodes and iron cathodes was used. Central composite design and response surface methodology (RSM) were applied to investigate the effects of six operational parameters, namely initial concentration of total phenols (TPh), total chromium (TCr), total ammonia nitrogen (TAN), flow rate (Q), current intensity (I), and electrode surface area (A). Effectiveness of the innovative cellulosic membrane was proven by considerable pH variations in the anolyte and catholyte chambers. A faster removal rate was observed for TPh and TAN, followed by TCr. The treatment level was very sensitive to Q and I in the studied ranges. RSM showed the removal efficiencies of 78.14%, 63.42%, and 86.09% for TPh, TCr, and TAN, respectively, are achieved under optimal conditions with consumption of only 9.03 kWh m^?3 electrical energy. Chlorinated compounds such as chloroform, 2,4-dichlorophenol, and chlorobenzene were detected as the degradation intermediates. According to the obtained results, electrolysis in the divided cell with cellulosic membrane is a practical, cost-effective method for advanced treatment of tannery effluents.     

Microalgae cultivation and culture medium recycling by a two-stage cultivation system

Nutrients and water play an important role in microalgae cultivation. Using wastewater as a culture medium is a promising alternative to recycle nutrients and water, and for further developing microalgae-based products. In the present study, two species of microalgae, Chlorella sp. (high ammonia nitrogen tolerance) and Spirulina platensis (S. platensis, high growth rate), were cultured by using poultry wastewater through a two-stage cultivation system for algal biomass production. Ultrafiltration (UF) or centrifuge was used to harvest Chlorella sp. from the first cultivation stage and to recycle culture medium for S. platensis growth in the second cultivation stage. Results showed the two-stage cultivation system produced high microalgae biomass including 0.39 g·L^–1Chlorella sp. and 3.45 g·L^–1S. platensis in the first-stage and second-stage, respectively. In addition, the removal efficiencies of NH₄⁺ reached 19% and almost 100% in the first and the second stage, respectively. Total phosphorus (TP) removal reached 17% and 83%, and total organic carbon (TOC) removal reached 55% and 72% in the first and the second stage, respectively. UF and centrifuge can recycle 96.8% and 100% water, respectively. This study provides a new method for the combined of pure microalgae cultivation and wastewater treatment with culture medium recycling.

Open image in new window

     

Enzymatic nitrous oxide emissions from wastewater treatment

Nitrous oxide (N₂O), a potent greenhouse gas, is emitted during nitrogen removal in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N₂O production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes’ activity is essential to minimize N₂O emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N₂O in terms of their nature, structure and catalytic mechanisms. The pathways of N₂O emission during wastewater treatment are briefly introduced. The key environmental factors influencing N₂O emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzymebased techniques for mitigating N₂O emissions directly or indirectly are proposed. Finally, areas for further research on N₂O release during wastewater treatment are discussed.

Open image in new window

     

Duckweed: an effective tool for phyto-remediation

Effective wastewater treatment through conventional methods that rely on heavy aeration are expensive to install and operate. Duckweed is capable of recovering or extracting nutrients or pollutants and is an excellent candidate for bio-remediation of wastewaters. Such plants grow very fast, utilizing wastewater nutrients and also yield cost effective protein-rich biomass as a by-product. Duckweeds being tiny surface-floating plants are easy to harvest and have an appreciable amount of protein (15%–45% dry mass basis) and a lower fiber (7%–14% dry mass basis) content. Besides nutrient extraction, duckweeds has been found to reduce total suspended solids, biochemical oxygen demand (BOD), and chemical oxygen demand in wastewater significantly. Depending on the initial concentrations of nutrients, duckweed-covered systems can remove nitrate (NO₃^?) at daily rates of 120–590 mg NO₃^? m^?2 (73%–97% of initial concentration) and phosphate (PO₄^?) at 14–74 mg PO₄^? m^?2 (63%–99% of initial concentration). Removal efficiencies within 3 days of 96% and 99% have been reported for BOD and ammonia (NH₃). Besides several genera of duckweeds (Spirodela, Lemna, Wolffia), other surface-floating aquatic plants like water hyacinth (Eichhornia) are well known for their phyto-remediation qualities.     

MBR工艺处理螺旋霉素制药废水过程中抗生素耐药菌与抗性基因的研究

抗生素废水含有大量的抗生素耐药菌(antibiotic resistant bacteria,ARB)与抗性基因(antibiotic resistance genes,ARGs),处理排放后可能增强受纳环境的微生物抗性,因此有必要深入研究抗生素废水处理过程中ARB与ARGs的削减效果及其影响因素。本研究采用膜生物反应器(membrane bioreactor,MBR)工艺处理螺旋霉素制药废水,考察了不同水力停留时间(hydraulic retention time,HRT)对ARB与ARGs削减效果的影响。结果表明,虽然在HRT=30 h时MBR对COD与氨氮的去除率略高于HRT=40 h,但HRT=40 h时,不仅总异养菌与肠球菌的去除效果更佳,出水肠球菌耐药率及携带的抗性基因检出率也更低,而且MBR对废水中erm B、erm F、erm X、mef A、ere A、mph B和转移元件ISCR 1、Tn 916/1545相对丰度的削减效果更好。这表明长HRT更有利于MBR工艺削减螺旋霉素废水的耐药菌与抗性基因。     

Cationic dye adsorption onto natural and synthetic zeolites in the presence of Cs+ and Sr2+ ions

Adsorption of diazine dye safranine O (SO) in the presence of Cs⁺ and Sr²⁺ ions was investigated onto natural and synthetic zeolites in order to predict competition of cationic organic species with their radionuclides, which are the main fission products released into the environment. Adsorption of SO was measured up to the 40th day and the surface-diffusion coefficients (D_s) were estimated by applying Nernst–Planck approximation based on a homogeneous-surface-diffusion model. The values of D_s were 10 times higher on natural zeolite than those of synthesized zeolite from fly ash (FA) under hydrothermal conditions. Similarly, distribution coefficients (K_D) were considerably higher on the clinoptilolite-type natural zeolite. The zeolitized product of FA is mainly composed of analcime and sodalite. SO adsorption on natural zeolite was not influenced by Cs⁺ and Sr²⁺ ions, but it decreased at high concentrations on synthetic zeolite. The higher influence of the Sr²⁺ ions on SO⁺ adsorption showed that they compete with each other for the same adsorption sites. These results suggested that natural zeolite cannot be used for remediation of wastewater polluted with Cs and Sr radionuclides in the presence of organic cations, whilst FA zeolite has a potential for Sr removal.     

Fe-pillared bentonite,a stable Fenton catalyst for treatment of petroleum refinery wastewater

Fe-pillared bentonite (Fe-Bent) was prepared by ion exchange as heterogeneous catalyst for degradation of organic contaminants in petroleum refinery wastewater. X-ray diffraction analysis showed the existence of α-Fe₂O₃. The effects of pH, H₂O₂ concentration, and catalyst dosage on the rate of lowering the chemical oxygen demand (COD) were investigated in detail. Removal efficiency of COD can be up to 92% under the following conditions: dosage of Fe-Bent 7 g L^?1, pH value 3, and H₂O₂ concentration 10 mmol L^?1. Fe-Bent showed good stability for the degradation of organics in petroleum refinery wastewater for five cycles. The adsorption of organics in wastewater onto Fe-Bent could be well described by a pseudo-second-order kinetic model.     

Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation

Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs with two ozonation stages with the observed rate constants of second stage ozonation, k _obs2, being higher than the observed rate constants in first stage, k _obs1. The k _obs1 of parabens was found to increase exponentially whilst k _obs2 was found to maximize at 35°C. Both k _obs1 and k _obs2 were found to decrease exponentially with respect to the initial concentration of parabens. Both pH and ozone dose showed positive effects on the rate of degradation. It was also observed that an ozone dose of 0.67 g/h resulted in the removal of 99% of parabens in 12 min, and also the removal of 61 and 32% of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, in 3 h of ozonation time for a 500 μM of solution of parabens.