Assessment of wastewater pollution in pig leather industry in China

Pig leather industry contributed significantly to the life of people all over the world, but serious water environmental problems have arisen. Investigation in tanneries with green pig hides in China showed that pollution resulted mainly from beamhouse operations. Assessment indicated that wastewater from pig‐hides processing had: (1) wide variations of pH, (2) high levels of sulfide (S^2?) and chromium, (3) high levels of neutral salts and ammonia nitrogen (NH ₄⁺‐N), (4) high levels of suspended solids (TSS) and oil & grease, and (5) low biodegradability. A tannery processing 10 000 pig hides per day generated chemical oxygen demand (COD) of 3.81–12.31 tonnes and NH ₄⁺‐N 0.27–1.06 tonnes, respectively. The pollution loads were equivalent to those of a city of 60 000–120 000 inhabitants, which has a COD of 3.9–10.56 tonnes/day and NH ₄⁺‐N of 0.462–1.164 tonnes/day, respectively (SEPAC). And nearly 30% of the tanneries discharged their wastewater by screening only or by primary treatment like coagulation–sedimentation, while the rest of them discharged directly into surface waters without any treatment.     

Combined biological treatment of high‐sulphate wastewater from yeast production

The wastewater from baker's yeast production contains above‐average concentrations of organic pollutants (25 000 mg/L total chemical oxygen demand, TCOD), nutrients (1500 mg/L N_tot, 100 mg/L P_tot) and sulphate (2900 mg/L SO₄^2?). Baker's yeast wastewater with a flow rate of 190 m³/day was treated in a mesophilic anaerobic/anoxic continuous stirred tank reactor (CSTR) system. At the expense of the reduction of trimethylglycine (or betaine‐component of sugar‐beet molasses) to other nitrogen‐containing compounds, it was possible to re‐oxidize the sulphides to elemental sulphur, remove them from the wastewater and increase biogas production. Therefore, the average removal efficiency in the anaerobic/anoxic system was 79% by TCOD, 100% by SO₄^2? in which the concentration of sulphides in the effluent did not exceed 50 mg/L. The application of this combined anaerobic/anoxic system to a full‐scale treatment plant supported biogas production up to 1300 m³/day, and the purification of wastewater was feasible without the use of granular sludge.     

Biological oxidation of high strength nitrogenous wastewater

A nitrification study was conducted in continuous flow stirred tank reactors using high strength nitrogenous wastewater (concentrated stream from a urea plant mixed with pharmaceutical wastewater). The reactors were operated at different solids retention times (SRT = 10–62.5 d) and hydraulic retention times (HRT = 1.5–2.1 d). Pharmaceutical wastewater was used as an organic carbon source to maintain a COD/TKN ratio of 1. The nitrification achieved at different SRTs varied from 87 to 99%. The nitrogen balance data show that ammonia assimilation and denitrification accounted for 4–53% of the total nitrogen removed. The yield coefficients and decay coefficients were Y_b = 0.5 (COD basis), k_db = 0.07 d⁻¹ (COD basis) for heterotrophs and Y_n = 0.15 (TKN basis), k_dn = 0.06 d⁻¹ (TKN basis) for nitrifiers respectively.     

Non‐steroidal anti‐inflammatory pharmaceutical wastewater treatment using a two‐chambered microbial fuel cell

The two‐chambered microbial fuel cell (MFC) was designed and used for studying the efficiency of the real wastewater treatment from a non‐steroidal anti‐inflammatory pharmaceutical plant as well as from synthetic wastewater containing diclofenac sodium (DS). The removal of the contaminants was expressed regarding chemical oxygen demand (COD) removal, as measured by spectrophotometry experiments. Moreover, the effect of two different types of the cathode on current characteristics and COD removal was investigated. This research showed that the Pt‐coated Ti cathode could lead to higher efficiency of both power density and COD removal. In this case, the results indicated that the maximum power density (P_max) was 20.5 and 6.5 W/m³ and the maximum COD removal was 93 and 78% for MFCs using real and synthetic wastewater, respectively.     

Application of response surface methodology for simultaneous carbon and nitrogen (SND) removal from dairy wastewater in batch systems

The application of batch systems to the direct treatment of dairy wastewater was investigated. Batch experiments were conducted to study the organics removal and simultaneous nitrification and denitrification (SND) process. The experiment was conducted by varying four independent parameters (mixed liquor suspended solids, chemical oxygen demand [COD]/N ratio, aeration time and cycling time), using a central composite design under response surface methodology. The process responses of five dependent parameters (COD, Total kjehldahl nitrogen (TKN), NO₃ ^?, effluent NO₃ ^? and effluent total nitrogen) were studied, and in each case, the percentage removal in batch runs was determined with each process displayed in contour plots. Finally, after optimizing the process conditions, the best treatment of dairy wastewater under optimized conditions was established and the responses were shown. This study shows that microbial granules cultivated under the alternating aerobic/anaerobic conditions in batch systems could efficiently remove organic carbon and convert all the ammonium to nitrogen gas.     

The preparation,characterization of FeC micro‐electrolysis materials using low‐cost biochar and the removal of ultra‐high COD pesticide wastewater

Two kinds of Fe? C micro‐electrolysis materials (Fe? C MEMs) named Fe⁰/Fe? C MEMs and Fe₃O₄/Fe? C MEMs were prepared using low‐cost biochar, chemical grade Fe⁰ powder and industrial iron powder. The Fe? C MEMs were characterized by XRD, SEM and FT‐IR. Meanwhile, the effects of sintering temperatures and mass ratios of Fe to C on the treatment high chemical oxygen demand (COD) pesticide wastewater were studied. The results display that the relative removal rate of COD reached 64% for Fe⁰/Fe? C MEMs when the sintering temperature was 400°C and the mass ratio of Fe to C was 1 : 1. For Fe₃O₄/Fe? C MEMs, and the mass ratio of Fe₃O₄ to C was 1 : 3, the relative removal rate of COD reached 63.71%. Hence, the chemical grade Fe⁰ powder could be replaced with industrial iron powder to achieve the goal of low‐cost treatment of the high COD pesticide wastewater.     

Using magnetic seeds to improve the aggregation and precipitation of nanoparticles from backside grinding wastewater

Backside grinding (BG) wastewater treatment typically requires large quantities of chemicals, i.e. polyaluminum chloride (PAC) coagulant and produces considerable amounts of sludge, increasing the loading and cost of subsequent sludge treatment and disposal processes. This study investigated the effects of the addition of magnetic seeds (FeO*Fe₂O₃) of selected particle sizes and of optimized combinations of magnetic seeds and PAC on the aggregation of silica nanoparticles from BG wastewater and on the sedimentation time at various pH values (5-9). The results show that the turbidity of BG wastewater was significantly reduced by the magnetic aggregation treatment. The dosage of PAC combined with 2.49 g L⁻¹ or 1.24 g L⁻¹ of magnetic seeds was reduced by 83% (from 60 to 10 mg L⁻¹) compared to the conventional process of using only PAC as a coagulant. The turbidity of the BG wastewater, initially 1900-2500 NTU, could also be successfully decreased about to 23 NTU by the addition of 3.74 g L⁻¹ magnetite (FeO*Fe₂O₃) only at pH 5 with an applied magnetic field of 1000 G. Different coagulation conditions using magnetic seeds combined with coagulant resulted in different aggregation performances. The treatment performance was more effective by using two-stage dosing, in which magnetic seeds and PAC were added separately, than that with one-stage dosing, where the magnetic seeds and PAC were added simultaneously during rapid mixing. The two-stage dosing allowed for a reduction in the optimum dosage of magnetic seeds from 3.74 g L⁻¹ to 2.49 g L⁻¹ or 1.24 g L⁻¹ without affecting performance when coupled with 0.01 g L⁻¹ of PAC coagulant. The developed method effectively reduced the production of waste sludge.     

Characterisation of the impact of coagulation and anaerobic bio-treatment on the removal of chromophores from molasses wastewater

The performance of a coagulation sequence using aluminium chlorohydrate (ACH) and a low MW polydiallyldimethylammonium chloride (polyDADMAC), and ferric chloride, for decolourising a high-strength industrial molasses wastewater was compared at bench scale. At their optimum dosages, ACH/polyDADMAC gave higher colour removal than FeCl₃ (45% cf. 28%), whereas COD reduction was similar (∼30%), indicating preferential removal of melanoidins (a major contributor to the colour) by ACH/polyDADMAC. Size exclusion chromatography and fluorescence excitation-emission matrix spectrometry suggested that chromophoric Fe-organic complexes were formed during FeCl₃ treatment of the molasses wastewater, which appeared to compromise decolourisation efficiency. Anaerobic bio-treatment of the wastewater enhanced the coagulation efficiency markedly, with FeCl₃ achieving 94% colour and 96% COD removal, while ACH/polyDADMAC gave 70% and 56% removal, respectively. The improved decolourisation was attributed to the decrease in low MW organics (<500 Da) and biopolymers by the biological treatment, leading to reduced competition with melanoidins for interaction with coagulant/flocculant. For both the wastewater and the biologically treated wastewater, ACH/polyDADMAC treatment gave flocs with markedly better settling properties compared with FeCl₃.     

Cultivation of anaerobic granular sludge in UASB reactors with aerobic activated sludge as seed

Methanogenic bacteria of 10⁸ g SS⁻¹ in the activated sludges from an aeration tank treating sewage and from a secondary sedimentation tank of an activated sludge plant treating textile dyeing wastewater were enumerated by the Most Probable Number (MPN) technique. By using the two activated sludges as the seed material, anaerobic granular sludges were obtained at 35°C in two lab-UASB reactors having volumes of 29 and 481, and treating a glucose molasses solution of 1000–3500 mg COD 1⁻¹ and citrate wastewater of 20,000–36,000 mg COD 1⁻¹ respectively. The characteristics of granulation using the activated sludge as the seed were similar to those using digested sewage sludge as the seed. It is shown that activated sludge is readily available seed material for an anaerobic reactor. The growth of methanogenic bacteria in the activated sludge can be attributed to the existence of some anaerobic nuclei in the activated sludge flocs. The factors for the cultivation of granular sludge by using the activated sludge are also discussed.     

Treatment of low strength domestic wastewater using the anaerobic filter

A laboratory scale anaerobic filter packed with synthetic high surface area trickling filter media was used to treat a low strength domestic wastewater averaging 288 mg 1⁻¹ COD. The filter was operated for 60 days after reaching steady-state at 20, 25, 35°C at a loading rate of 0.02 lb COD ft⁻³ day⁻¹ and 24 h hydraulic retention time. Filter effluent BOD₅ averaged 38 mg 1⁻¹ providing an average removal rate of 79%, and effluent COD averaged 78 mg 1⁻¹, corresponding to a 73% removal rate. Removal efficiencies showed very little sensitivity to daily fluctuations in influent wastewater quality. The filter performance at 25 and 35°C was not significantly different, but BOD and TSS removal efficiency declined a: 20°C. Gas production averaged 0.027 ft⁻³ of gas per ft³ of influent wastewater, or 1.875 ft³ of gas per pound of influent COD. Gas composition averaged 30% nitrogen, 65% methane, and 5% carbon dioxide. Ammonia nitrogen and sulfides both increased during treatment. It is concluded that the anaerobic filter is a promising candidate for treatment of low strength wastewaters and that post treatment for sulfides and ammonia may be necessary.     

Fermentation of food industry wastewater

Treatment of wastewater formed during production of citric acid and fodder yeast was carried out under dynamic conditions on a laboratory scale in an anaerobic upflow biofilter. The bioreactor was run at a temperature of 36°C. Methane fermentation of wastewater from citric acid production proceeded with a high yield. Removal of 73% COD and 73% BOD₅ was achieved at a biofilter loading rate of 3.16 kg COD/m³ d and a 48-h hydraulic retention time of the wastewater. In addition, 65 and 70% reductions of COD and BOD₅, respectively, were attained with respect to wastewater from fodder yeast production at a biofilter loading rate of 3.00 kg COD/m³ d and a 60-h hydraulic retention time. The methanogenesis process yielded 0.32 m³ CH₄/kg of removed COD for citric acid wastewater and 0.34 m³ CH₄/kg of removed COD for wastewater from the fodder yeast production plant. Microbiological reduction amounting to 50% of sulphates was found to occur in wastewater from the fodder yeast production plant at an initial sulphate concentration of about 4500 mg SO₄²⁻/dm³.As determined by Oleszkiewicz's formula, the specific coefficients of the reaction rates, k, were 2.90 and 2.02 kg COD/m³ d depending on the type of wastewater. Consequently, it has been shown that the anaerobic upflow biofilter is suitable for treating wastewater produced during molasses processing. Attention should also be drawn to its unique and simple construction and the relatively low power demand required to operate this unit. Wastewater recirculation was not required in the unit.     

合流制溢流调蓄处理工艺效果评估及优化对策

针对初期雨水及合流制溢流水质和水量波动大而引起的调蓄工程处理能力不足、运行能耗高及难以有效收集高负荷合流制溢流污水等问题,通过对不同时期进入调蓄工程的合流制溢流水质和水量特征的分析,结合调蓄工程处理工艺的沿程水质分析,考察了"微砂高效沉淀池+接触氧化池+D型滤池"工艺对合流制溢流的实际处理效果。结果表明,初期雨水及合流制溢流均呈水质和水量波动大、高氨氮、低COD的特征,氨氮是调蓄处理工艺出水水质达标的关键指标;同时,生化处理单元进水COD浓度低的特征不利于接触氧化池的生物挂膜,降低了工艺的实际处理能力。因此建议:(1)在接触氧化池后设置混凝加药装置,以保证出水SS和TP达标排放;(2)接触氧化池采用多点进水方式,并预留碳源投加装置;(3)增加精确曝气控制系统,实现节能降耗。     

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD₅/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L⁻¹, 0.48 for BOD₂₁/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS⁻¹ h⁻¹.     

ACE工艺用于氮肥生产企业废水处理工程

介绍了ACE工艺在氮肥生产企业废水处理工程中的应用情况并对存在的典型问题提出了解决措施.实际工程表明,ACE工艺在进水COD≤1 000 mg/L、NH3-N≤250 mg/L时,出水水质优于国家有关合成氨工业废水的一级排放标准.其主要设计参数对于类似高氨氮有机废水的处理具有一定的借鉴意义.     

Treatment of pharmaceutical wastewater (herbal) by a coagulation/flocculation process

Pharmaceutical factory wastewater (herbal nature) poses pollution problem due to its high COD and BOD. Moreover the characteristics of the wastewater depicts wide variation due to variation in the type of medicines manufactured and raw material utilization. Addition of solvents and oils as per the requirement also add to the pollution load. Because of this problems the conventional treatment units which employ activated sludge process (ASP) and trickling filter for the pharmaceutical factory (herbal) effluent treatment usually malfunctions. It was thus proposed to subject the wastewater to physico‐chemical treatment, using different coagulants and coagulant aids. Commonly available coagulants like lime, alum, ferrous sulphate, ferric chloride, polyaluminium chloride (PAC) and also polyelectrolyte were studied.

Results indicated that this wastewater is amenable to physico‐chemical treatment, and can be applied both as a pretreatment technology or as a polishing treatment. Lime: Alum: Polyelectrolyte resulted in good and most economical removals of SS, COD and BOD of 69.75%, 82.51% and 86.72%, respectively, at a dose of 300 : 100 : 0.1 mg/l, respectively.

The paper discusses in detail the results obtained with other coagulants and their comparative efficiency.     

Improve effluent water quality at Abu‐Rawash wastewater treatment plant with the application of coagulants

This research investigated a process to improve the Abu‐Rawash WWTP effluent water quality with the application of aluminum chloride (AlCl₃); in turn, this improvement will lead to improve water quality at the El‐Rahawy drain and in the Rosetta branch of the Nile River. Sewage samples were collected from the effluent of the grit removal chamber. Jar tests were performed to estimate the coagulant dosage required to obtain acceptable treatment. To prove the efficiency of the AlCl₃ in wastewater treatment, a comparison was conducted between AlCl₃ and other common coagulants used in wastewater treatment which include ferrous sulfate (FeSO₄), ferric sulfate (Fe₂(SO₄)₃) and ferric chloride (FeCl₃). Results showed AlCl₃ was more cost‐effective and efficient in wastewater treatment than these three iron‐based coagulants. A paired‐sample t‐test was also performed to rank the performance of the various coagulants tested. The t‐test has also confirmed that the AlCl₃ has the highest performance over those coagulants.     

Enhanced efficiencies of sludge dewatering and domestic wastewater treatment by using the bioflocculant from rice stover

Potential of a bioflocculant from rice stover was studied in sludge dewatering and domestic wastewater treatment. Production of this bioflocculant showed good correspondence to cell growth, after fermentation for 60 h, the fermentation liquor was obtained, from 1.0 L of which a value of 2.37 g bioflocculant can be extracted, and the main backbone of this bioflocculant was polysaccharides. Without adjusting the sludge's initial pH value of 6.5, when incubated with 18 mg/L of this bioflocculant, dry solids (DS) and specific resistance to filtration (SRF) of the typical wastewater activated sludge reached 18.5% and 4.7 × 10¹² m/kg, respectively, which was better than the ones achieved by Al₂(SO₄)₃ and FeCl₃ flocculants. For domestic wastewater treatment, after treated by 12 mg/L of this bioflocculant at pH value of 7.5, removal efficiencies of chemical oxygen demand (COD) and turbidity can reach 91.8 and 89.7%, respectively, which were better than the ones achieved by the traditional flocculants such as Al₂(SO₄)₃, FeCl₃, and polyaluminum chloride (PAC). This study suggested that the bioflocculant from rice stover has great potentials as an alternative flocculant to conventional flocculants in sludge dewatering and domestic wastewater treatment.     

An adsorption-photocatalysis hybrid process using multi-functional-nanoporous materials for wastewater reclamation

In this study, two of our recently developed laboratory scale wastewater treatment systems, fluidised-bed reactor (FBR) using formulated clay mixture absorbents (clay-FBR adsorption) and an annular slurry photoreactor (ASP) using TiO₂ impregnated kaolin catalysts (TiO₂-K-ASP) were integrated as an adsorption-photocatalysis hybrid process to treat municipal wastewater as alternative secondary and tertiary treatment for wastewater reclamation. Primary effluent from sewage and secondary effluent from a membrane bioreactor treatment process were used to assess chemical removal capabilities of the FBR and ASP systems, and the hybrid process. The formulated clays-FBR system demonstrated the prevailing removal efficiency toward PO₄³⁻, NO₃⁻ and suspended solids. The TiO₂-K-ASP showed superior degradation of dissolved organic content; while the presence of inorganic ions caused a detrimental effect on its performance. The integration of the adsorption and degradation system as a hybrid treatment process resulted in a synergetic enhancement for the chemical removal efficiency. Complete elimination of PO₄³⁻ content was obtained in the adsorption stage; while 30% and 65% NO₃⁻ removal were obtained from the hybrid treatment of the primary and secondary effluents, respectively. The corresponding COD reduction during the photodegradation was further investigated by the high-performance size exclusion chromatography technique, where it revealed the shift of apparent molecular weight of the dissolved organic contaminants toward the smaller region. This present study demonstrated that this adsorption-photocatalysis hybrid technology can be used as a feasible alternative treatment process for wastewater reclamation.     

云南某废弃菜叶处理厂废水处理工程实例

废弃菜叶处理(破碎+厌氧产沼气)过程中产生的废水是一种污染物浓度较高、C/N偏低的废水。云南某废弃菜叶处理厂废水处理工程采用A²O²(二级O池为MBR膜池)工艺,以强化氮的脱除,保证出水TN的达标。对A²O²工艺的启动特性、运行效果及运行费用组成进行了分析。在工艺启动过程中,COD的去除效率可以稳定在70%以上;当硝化反应发生后,对NH₄⁺-N的去除率>99.5%;投加一定量的碳源后,对TN可以达到较高的去除率。稳定运行后,出水的COD、NH₄⁺-N、TN和TP分别稳定在300、10、45、5 mg/L以下,满足《污水排入城镇下水道水质标准》(GB/T 31962—2015)的C级标准。经测算,处理成本为27.564元/m³。     

Electrochemical treatment of chemical oxygen demand in produced water using flow‐by porous graphite electrode

Produced water is the largest wastewater stream generated in the oil and gas industries. In this study, experiments were carried out using a bench‐scale electrochemical cell using flow‐by porous graphite electrode, for oxidation of organic matter in produced water which was collected from natural gas processing field (real sample). The effect of anodic current density and influent feed flow rate on chemical oxygen demand (COD) removal efficiency, and energy consumption were investigated. The maximum removal efficiency of 66.52% was obtained for a flow rate of 50 mL/min, current density of 1.41 mA/cm² and pH of 7.3 for an influent COD of 2845 mg O₂/L. The energy consumption at these conditions was 2.12 kWh/kg_COD.