Optimization of the coagulation-flocculation process for pulp mill wastewater treatment using a combination of uniform design and response surface methodology

Pulp mill wastewater was treated using the coagulation-flocculation process with aluminum chloride as the coagulant and a modified natural polymer, starch-g-PAM-g-PDMC [polyacrylamide and poly (2-methacryloyloxyethyl) trimethyl ammonium chloride], as the flocculant. A novel approach with a combination of response surface methodology (RSM) and uniform design (UD) was employed to evaluate the effects and interactions of three main influential factors, coagulant dosage, flocculant dosage and pH, on the treatment efficiency in terms of the supernatant turbidity and lignin removals as well as the water recovery. The optimal conditions obtained from the compromise of the three desirable responses, supernatant turbidity removal, lignin removal and water recovery efficiency, were as follows: coagulant dosage of 871 mg/L, flocculant dosage of 22.3 mg/L and pH 8.35. Confirmation experiments demonstrated that such a combination of the UD and RSM is a powerful and useful approach for optimizing the coagulation-flocculation process for the pulp mill wastewater treatment.     

The risks from airborne asbestos in the urban environment

The objective of this full‐scale study is to determine the treatment performance of the activated sludge process for treating low strength municipal wastewater. The plant is located in Painesville, Ohio, and discharges its treated effluent into Grand River. The average plant wastewater flow was 3.43 MGD (million gallons per day). The plant performance was evaluated for a 12‐month period in 1989. The low strength municipal wastewater contained 104 mg/L TSS (total suspended solids), 105 mg/L BOD (biochemical oxygen demand), 17.76 mg/L TKN (total kjeldahl nitrogen), 9.66 mg/L NH₃‐N, and 3.90 mg/L P (phosphorus). The treatment performance after various degrees of treatment is as follows: primary treatment: 30% BOD and 54% TSS removal, secondary treatment: 97% BOD and 87% TSS removal, and tertiary treatment: 98% BOD and 98% TSS removal. The primary effluent contained 73 mg/L BOD and 48 mg/L TSS; the secondary effluent contained 3 mg/L BOD and 13 mg/L TSS; and the final effluent contained 2 mg/L BOD and 2 mg/L TSS. The effluent contained 0.22 mg/L NH₃‐N and 0.49 mg/L P, which were far below the US EPA standard of 10 mg/L BOD, 10 mg/L TSS, 1 mg/L NH₃‐N, and 1 mg/L P.     

Optimization of the landfill leachate treatment by the Fenton process

The Fenton process was used with the objective of improving the biodegradability of the leachate pretreated biologically up to a value compatible with a subsequent biological treatment. The optimum reaction and settlement pH was 3, both for the organic matter removal and for the improvement of the biodegradability. The chemical oxygen demand (COD) removal increased at increasing Fe²⁺ dosages, from 75.6% for 300 mg/L to 89.0% for 1400 mg/L. The most significant enhancement (84.8%) was obtained with 800 mg Fe²⁺/L. However, the biological oxygen demand/chemical oxygen demand ratio (BOD/COD) was almost the same at all the Fe²⁺ dosages, around 0.29. Moreover, varying the H₂O₂ concentration between 600 and 3600 mg/L, COD removal percentages were between 85.9 and 89.0%. However, the BOD/COD ratio increased at increasing H₂O₂ dosage up to 3000 mg/L, from 0.12 at 600 mg/L to 0.29 at 3000 mg/L.     

改性钢渣的制备及其吸附除磷性能

研究了改性钢渣吸附除磷影响因素、等温吸附线特征和吸附动力学,并对生物处理后的出水进行吸附除磷研究。结果表明:在初始磷浓度10mg/L,投加量10g/L、pH为7时,改性钢渣吸附后总磷浓度为0.687mg/L,去除率达93%;改性钢渣对磷的吸附符合Langmuir模型,理论饱和吸附量是1.977mg/g,吸附动力学符合准二级动力学模型(R20.99);实际生活污水的吸附除磷中,投加量为50g/L,反应2h后出水总磷浓度达到《城镇污水处理厂污染物排放标准》(GB18918—2002)一级B标的排放要求。     

二次通用旋转组合设计下磁絮凝工艺处理河道水效果

在实验室运用二次通用旋转组合设计研究苏州河道水处理工艺,系统分析了磁絮凝工艺处理苏州河道水的四个影响因素(PAC投加量、PAM投加量、磁粉投加量、沉淀时间)对磁絮凝效果的影响效应。并运用方差分析、回归模型方程分析、单因子效应分析以及双因素交互效应分析,得出最佳工况为PAC投加量15 mg/L、PAM投加量0.58 mg/L、磁粉投加量2.7 mg/L、沉淀时间2.1 min,此时理论上浊度可达到0.73 NTU,浊度去除率为97.2%,用此参数进行试验,得到实际浊度为0.82 NTU,实际浊度去除率可达96.9%。     

新生态水合氧化铁去除水中磷酸根的效能研究

以新生态水合氧化铁(FHIO,由高铁酸钾和氯化亚铁配制)为混凝剂,考察了对水中磷酸根的处理效能,以及有机物浓度、pH、温度、浊度等参数对其去除磷酸根的影响。通过对原水pH和浊度变化的分析,发现FHIO的水解过程不同于普通铁盐,可形成细小、比表面积大、吸附能力强的铁氧体。在投加氯化铁进行混凝时,随着投量(6、7、8mg/L)的增加,对磷酸根的去除率分别达到了54%、59%、70%。而在相同的总铁投量下,FHIO对磷酸根的去除率分别提高了11%、13%、9%。水中有机物浓度的增加,对FHIO的除磷效果有一定的影响,这是因为有机物在一定程度上抑制了Fe(Ⅱ)的氧化,间接地影响了FHIO的生成,从而降低了除磷效果。在较低温度、pH和浊度时,FHIO对磷酸根的去除效果明显优于单独铁盐的,这是由于FHIO的无定形状态和细小的颗粒度决定其受这些因素的影响较小。     

Fenton试剂强化铁炭微电解预处理高浓有机废水

研究了Fenton试剂法强化铁炭微电解工艺对高浓度难生化有机废水的预处理效果。结果表明，当原水COD在9000mg／L、铁炭微电解反应时间为100min、pH值为2．2时，铁炭微电解对原水COD的去除率〉45％；铁炭微电解出水再投加240mg／L的H2O2（30％）进行Fenton试剂法处理，常温下反应50min对原水COD的去除率可提高到75％以上。铁炭微电解＋Fenton试剂联合工艺的除污效果好、运行稳定、成本低廉，适宜对高浓度难生化有机废水的预处理。     

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.     

Combining magnesium ammonium phosphate precipitation with membrane processes for ammonia removal from methanogenic leachates

Chemical precipitation of ammonia as magnesium ammonium phosphate (MAP) from methanogenic leachates can be a competitive alternative to biological ammonia removal. Potential for trading of the precipitate as a fertiliser defines the economics of the process. The precipitate from a landfill leachate often containing organics and heavy metals as impurities with unknown risks limits its possibility for agricultural use. This study combines MAP precipitation with membrane processes and investigates the influence of wastewater matrix, solution pH and dosage ratio of chemicals (Mg²⁺ : ) on the precipitate purity through lab scale semibatch experiments. Under similar experimental conditions (pH 8.5 and 1 : 1 Mg²⁺ : molar dosage), the precipitates from raw leachate and nanofiltration (NF) permeate showed MAP contents of 65 and 90%, respectively, correspondingly with about 8300 and 1600 mg TOC/kg_precipitate. For precipitation from NF permeate, precipitation at pH 8.0 with 1 : 1 dosage ratio and pH 8.5 with 1 : 0.9 dosage ratio gave precipitates each with about 97% purity.     

Enhanced electrocoagulation–electroflotation for turbidity removal by Opuntia ficus indica cladode mucilage

The optimisation of the electrocoagulation‐electroflotation (EC‐EF) process assisted by the mucilage of the Opuntia ficus indica (OFI), on the turbidity removal was performed through the response surface methodology (RSM). For a solution of 300 mg/L of silica gel, high turbidity removal (93.14% ± 1.31) was obtained under the optimal conditions of 2.5 mg/L, 21.2 V, 9.65 and 2.61 mS/cm for the mucilage concentration, voltage, pH and conductivity, respectively, this experimental value was close to the predicted value of 92.96% ± 0.3. OFI mucilage increases turbidity removal efficiency and reduces specific energy consumption at a fixed current density. The turbidity removal of the EC‐EF process was improved by 30.94% compared with the conventional EC–EF (EC–EF without OFI mucilage) which shows 62.02% ± 1.45 of turbidity removal.     

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.     

PAFS-PDMDAAC复合絮凝剂的除磷效果研究

针对生物除磷稳定性差、效果欠佳的问题，研发了PAFS—PDMDAAC复合絮凝剂，考察了复合絮凝剂中PDMDAAC的复合比、污水pH值及复合絮凝剂投量对除磷效果的影响。结果表明，将絮凝剂配成质量分数为10％的液体，在PDMDAAC复合比为5％、液体复合絮凝剂投量为1．6～2．4mL／L、污水pH值为7～13的优化条件下，对模拟废水中磷的去除率〉97％，除浊率〉99．40％。同时考察了在优化试验条件下复合絮凝剂对实际污水的除磷效果，结果表明，除磷率达98．42％，除浊率为98．53％，出水中磷浓度可达到国家一级排放标准。     

不同混凝剂强化除藻、除浊的研究

采用聚合氯化铝(PAC)、聚合氯化铝铁(PAFC)、聚合硫酸铁(PFS)、聚合硫酸铝(PAS)和硫酸铝(AS)五种混凝剂对某含藻湖水进行强化混凝除藻、除浊试验研究,考察了混凝剂种类及投量、原水pH、沉降时间等因素对强化混凝效果的影响。结果表明,五种混凝剂的综合除藻、除浊性能排序为:PACPAFCPFSPASAS;在原水pH值为5~9的范围内,含铁混凝剂PFS和PAFC对pH的适应性较强,且在pH值为5~7的弱酸性条件下,PFS的除藻、除浊性能最优,当其投量为4 mg/L时,除藻率近80%,除浊率可达80%以上;而在pH值为7~9的弱碱性条件下,PAC则表现出更好的除藻、除浊效果,当其投量为4 mg/L时,除藻率和除浊率可分别达到83%和90%;AS对pH的适应性最差,其除藻、除浊效果最差;另外,五种混凝剂的除藻率、除浊率均随沉降时间的延长而增大,最佳沉降时间为20 min。     

高分子重金属絮凝剂PEX处理电镀废水研究

以电镀废水为处理对象，研究了高分子重金属絮凝剂PEX对废水中重金属离子、浊度及有机污染物的处理效果；同时考察了废水pH值对重金属离子去除效果的影响及重金属离子的回收率。结果表明，当废水pH≥6．0时，pH值的变化对重金属去除率的影响不大；在pH=6．5～7、PEX的投量为160mg／L时，对镍的去除率〉95％，对铜和铬的去除率〉99％，对有机物的去除率为64％；重金属离子的回收率随盐酸浓度的增大而提高，当盐酸浓度为15％时对镍离子的回收率为70％，对铜离子的回收率为24％左右。     

Optimization of phenol removal from wastewater by activation of persulfate and ultrasonic waves in the presence of biochar catalyst modified by lanthanum chloride

In this paper, the effects of phenol concentration, pH, catalyst dose, persulfate concentration, temperature and contact time on the phenol removal from wastewater by activation of persulfate (S₂O₈^?2) in the presence of biochar modified by lanthanum chloride and ultrasonic waves (US) are optimized. Experimental design and optimization were carried out by response surface methodology. The optimum conditions for the maximum phenol removal were obtained pH of 4, phenol concentration of 86 mg/L, catalyst dose of 43 mg/L, persulfate concentration of 86 mg/L, temperature of 41 °C and contact time of 63 min. The optimum phenol removal from synthetic wastewater was attained 97.68%. Phenol removal by the mentioned system was fitted with the first‐order kinetic model. The combination of the ingredients of ‘S₂O₈^?2/US/Biochar‐LaCl₃’ system had a synergistic effect on the phenol removal.     

高铁酸钾深度处理垃圾渗滤液的试验研究

采用自制的高铁酸钾深度处理垃圾渗滤液二级生化处理出水,考察了处理效果。结果表明,高铁酸钾投量、pH值和反应时间对COD和NH3-N的去除效果均有显著影响。当pH值为6,高铁酸钾投量为110 mg/L,反应时间为30 min时,对COD的去除效果最好;当pH值为8,高铁酸钾投量为125 mg/L,反应时间为24 min时,对NH3-N的去除效果最佳。渗滤液初始COD浓度低不利于高铁酸钾对COD的去除。     

PAC和PAM复合混凝剂处理垃圾渗滤液的研究

通过投加混凝剂聚合氯化铝(PAC)和助凝剂聚丙烯酰胺(PAM)对垃圾渗滤液进行混凝沉淀处理,根据单因素和正交试验确定其最佳工艺条件.结果表明,混凝的最佳条件:PAC投加量为750 mg/L、PAM投加量为15 mg/L、快速(150 r/min)搅拌1 min、中速(45 r/min)搅拌6min、慢速(35 r/min)搅拌7 min、在快速混合之后投加助凝剂.在该处理条件下,系统对垃圾渗滤液中COD和浊度的去除率达到最大,分别为27.45%和65.80%.     

Algal settling ponds contribute to final effluent quality of integrated algal pond systems for municipal sewage treatment

Appropriate wastewater technologies and sound management are crucial to global water quality and conservation. The integrated algal pond system (IAPS), considered an efficient, passive and low-cost wastewater treatment technology for peri-urban spaces, is perceived to yield a final effluent unsuitable for discharge. Experiments were carried out to challenge the prevailing perception that algal-based wastewater treatment processes and in particular IAPS produce an effluent that does not always meet national and/or regional regulatory standards. Formation of a microalgal–bacterial floc (MaB-flocs) and settleability together with biomass removal from algal settling ponds (ASPs) is shown to reduce total suspended solids (TSS) from >50 to <20 mg L⁻¹. Thus, production of a readily settleable MaB-floc coupled with removal of settled biomass from ASP ensures that final effluent TSS remains below the general limit of 25 mg L⁻¹ and yields an effluent suitable for either irrigation or discharge.     

Removal of metribuzin by sulfate radical‐based photooxidation: multi‐objective optimization by central composite design

The objective of this study was to optimize the experimental conditions for maximum removal efficiency and minimum operating cost for removal of metribuzin pesticide from aqueous solution. Central Composite Design model was applied as Response Surface Design. In the model, independent parameters were ultraviolet irradiation time, persulfate anion dosage, TiO₂ dosage, pH and response parameters were metribuzin removal (%) and operation cost. Analysis of variance (ANOVA) was used to describe the significance level of factors on the multiple performance characteristics considered. It has been found that the most suitable model is the quadratic model to explain the both responses and the correlation coefficient (R²) of the relationship between the actual metribuzin removal and the predicted removal was calculated as 0.9518. As a result of multi‐optimization, removal efficiency of 84.59 (%) and operation cost of 4.44 (€/g) were obtained at ultraviolet irradiation time at 12.03 min, persulfate anion concentration at 4.909 g/L, TiO₂ concentration at 0.197 g/L and pH at 4.     

Batch coagulation of a lagoon for fecal coliform reductions

The research examined the factors affecting fecal coliform removal from lagoon wastewater by batch treatment with aluminum sulphate. Laboratory experiments based on factorial designs and jar tests were used to determine the statistically significant factors controlling the removal of fecal coliform bacteria. Temperature, chemical dose, pH, rapid mixing and flocculation were examined at two different laboratory scales. The results indicated that alum dose and pH were the only significant parameters. A design chart was developed for the wastewater tested enabling dose determination for a desired fecal coliform reduction. This chart was used to select the dose for a full scale field trial to reduce fecal coliforms to < 10 per 100 ml. The design dose was 300 mg 1⁻¹ Al₂(SO₄)₃·18 H₂O and a final pH of 6.4 was predicted.The field trial used liquid alum (Al₂(SO₄)₃·14.2 H₂O) delivered by tanker truck and distributed by motor boat. The treatment reduced fecal coliforms by 99.9%, total phosphorus by 97%, total suspended solids (TSS) by 90% and 5-day carbonaceous biochemical oxygen demand (CBOD₅) by 35%.The cost of treatment for labour and materials was $CDN 0.07 m⁻³.