Treatment of wastewater from an oil and soap factory via dissolved air flotation

Highly polluted wastewater from oil and soap factories has been treated via coagulation followed by dissolved air flotation. Ferric chloride and alum were used as coagulants at their optimal pH value and dosages. Factors affecting the efficiency of the dissolved air flotation process, such as detention time and air-solids ratio, have been investigated. The results obtained showed that this process proved to be very efficient in removing the organic contaminants. The oil removal value reached 99.1%. The COD, BOD, and turbidity removal achieved 94.5%, 96% and 99.3%, respectively.     

Removal of nutrients and heavy metals from anaerobic waste by aerobiological treatment

This study was conducted to investigate the effectiveness of aerobic biological treatment in removal of nitrogen, phosphorous, and heavy metals from a unique anaerobic liquid waste, produced at a solid waste-to-methane anaerobic digestion facility. Laboratory scale continuous flow activated sludge reactors were employed in this study. The liquid waste has moderate BOD/COD ratio with BOD concentration of 1300 mg/L and high concentration of essential nutrients, making the liquid waste biologically treatable. Results showed that aerobic biological treatment can remove nitrogen and phosphorous on the order of 85%. Metal removal efficiencies vary widely for 11 metals studied in this investigation.     

Mosquito larvae density and pollutant removal in tropical wetland treatment systems in Honduras

Constructed wetlands offer a low-cost wastewater treatment option for tropical developing countries. The vast majority of published treatment wetland research has been conducted in temperate regions. Because the function of treatment wetlands is related to the environmental conditions, more research specific to the tropics should be completed. A six-cell free water surface (FWS) wetland mesocosm was constructed in Santa Rosa de Copán, Honduras that received input from an open-sewer/wastewater-impacted stream. Three cells were planted with Typha domingensis Pers., and three cells were left unplanted. Both planted and unplanted wetlands were constructed with three different surface areas to concurrently study different hydraulic retention times (HRTs) and hydraulic loading rates (HLRs). Results from 6 months of operation showed improved water quality and mosquito larvae populations affected by their specific environment. Five-day biochemical oxygen demand (BOD) removal appeared to be proportional to HRT and HLR, and BOD concentration in the effluent was higher in unplanted cells than in planted cells (P<0.05). BOD removal approached 60% for greater than 3.5 days HRT. Total phosphorus (P) removal and coliform bacteria removal were found to be correlated with pollutant load, and P removal was found to be correlated with HRT but not HLR. A second municipal wastewater FWS treatment wetland in Copán Ruinas, Honduras that had been established for 15 years, was also evaluated. BOD removal in the Copán Ruinas system was determined to be 93% with 2.6 day HRT. These pollutant removal rates are higher than would be expected in temperate regions. Mosquito larvae density was correlated with depth of the wetland. Mosquito larvae densities were higher in cells that were operating below design depth of 0.2 m (P<0.005). Results indicate that it is possible to design FWS wetlands in the tropics for effective BOD removal and reduced mosquito larvae development.     

Ultrasonically enhanced anaerobic digestion of waste activated sludge

Anaerobic digestion is increasingly applied to stabilise sludge and to reduce operating costs of the wastewater treatment plant by generating biogas, considered as a sustainable energy source. The process suffers from many drawbacks such as slow and incomplete degradation rates, the result of the slow and rate‐limiting sludge hydrolysis step, due to the low biodegradability of the cell walls and the presence of extra‐cellular biopolymers.

Methods to enhance the biogas formation should hence make the substrate more accessible to the anaerobic micro‐organisms. Research on increasing the biogas production is extensive, with low‐frequency ultrasound treatment emerging as the technical and economic most appropriate technology. Although ultrasound is now widely applied in practice, underlying phenomena and optimum operating conditions are still open to debate. Laboratory ultrasound treatment was coupled with digestion experiments (at 37°C) using 12 parallel digesters, two of them being used as control digesters with untreated sludge.

The present paper demonstrates that ultrasound treatment can – within specific ranges of energy‐input – achieve (i) an increased disintegration of the sludge, as witnessed by an increasing soluble COD‐fraction accompanied by an increasing presence of BOD; (ii) an increased release of volatile fatty acids as a result of the oxidising radicals being formed through cavitation; and (iii) a slightly reduced dewaterability of the residual sludge, needing an increased dosage of poly‐electrolyte to obtain a high degree of cake dryness.

As pre‐treatment to digestion, ultrasound enhances the biogas production by more than 40% at low specific energy‐inputs (SE), and approximately 15% at higher SE‐values.     

Treatment of olive mill effluents Part II. Complete removal of solids by direct flocculation with poly-electrolytes

The pre-treatment of three different olive oil processing effluents by means of direct flocculation (i.e. without prior coagulation) was investigated. Four cationic and two anionic poly-electrolytes were tested and most of them were found capable of removing nearly completely total suspended solids (TSS) as well as reducing considerably the concentration of chemical (COD) and biochemical oxygen demand (BOD(5)) without altering solution pH. Flocculant dosage was crucial to achieve effective separation. For three cationic and one anionic poly-electrolytes, the minimum dosage required to initiate separation was about 2.5-3 g/L. The remaining two poly-electrolytes failed to cause separation even at dosages as high as 7 g/L. Lime and ferric chloride were also tested as reference coagulants and found quite effective in terms of TSS removal although the degree of COD reduction was generally lower than that with poly-electrolytes. However, lime treatment would require greater dosages and longer treatment times than that with poly-electrolytes and would also increase considerably solution pH. A preliminary cost analysis showed that lime treatment for complete solids removal was generally less costly than that with poly-electrolytes presumably due to its low market price. Nonetheless, cost-benefits may be defied by several drawbacks associated with the use of lime.     

Toxicity removal from hard board wastewater

The rapid growth of industry in Egypt in recent years has made industrial pollution an important issue. During the past decade fish production in some canals and lakes have virtually ceased due to the discharge of industrial and agricultural wastewater. The alternatives under study include effluent treatment before discharge to receiving water. Highly polluted wastewater from a hard board mill was treated using the activated sludge process. Factors affecting the efficiency of the treatment were detention time and organic loading rate. The results indicated that BOD and phenol reduction reached 82% and 94% respectively. when the organic loading rate was 0.1 (kg BOD/kg SS). The process proved to be successful in completely eliminating the toxicity effect of the waste on Nile fish (Tilapia nilotica).     

Potential use of solar energy for waste activated sludge treatment

The use of solar energy as a disintegration unit operation for waste activated sludge was tested in a pilot plant. The effect of the treatment process on chemical oxygen demand (COD), total suspended solids (TSS), settling time and filtration index was investigated in single (solar) and sequential processes (solar & biological). Solar oxidation was found to be a good sludge disintegration technology. Available solar photons were utilised to degrade the soluble organic matter and release the cell liquids. The highest COD and TSS removal efficiencies were obtained by the month of June. Sequential process efficiencies were related to accumulate solar photons, aerobic treatment time and operational condition. Sequential process resulted in COD and TSS removal efficiency of 16% and 13%, respectively. Increasing aerobic treatment time and/or mixing the oxidised sludge with fresh sludge improved COD and TSS removal efficiencies to 23% and 27%, respectively. The use of sequential processes improves the settling tendency of sludge by bio-oxidation of the released portions and eliminates protein charge effect on sludge settling.     

Nonylphenol in the environment: a critical review on occurrence, fate, toxicity and treatment in wastewaters

Nonylphenol is a toxic xenobiotic compound classified as an endocrine disrupter capable of interfering with the hormonal system of numerous organisms. It originates principally from the degradation of nonylphenol ethoxylates which are widely used as industrial surfactants. Nonylphenol ethoxylates reach sewage treatment works in substantial quantities where they biodegrade into several by-products including nonylphenol. Due to its physical-chemical characteristics, such as low solubility and high hydrophobicity, nonylphenol accumulates in environmental compartments that are characterised by high organic content, typically sewage sludge and river sediments, where it persists. The occurrence of nonylphenol in the environment is clearly correlated with anthropogenic activities such as wastewater treatment, landfilling and sewage sludge recycling. Nonylphenol is found often in matrices such as sewage sludge, effluents from sewage treatment works, river water and sediments, soil and groundwater. The impacts of nonylphenol in the environment include feminization of aquatic organisms, decrease in male fertility and the survival of juveniles at concentrations as low as 8.2 mug/l. Due to the harmful effects of the degradation products of nonylphenol ethoxylates in the environment, the use and production of such compounds have been banned in EU countries and strictly monitored in many other countries such as Canada and Japan. Although it has been shown that the concentration of nonylphenol in the environment is decreasing, it is still found at concentrations of 4.1 mug/l in river waters and 1 mg/kg in sediments. Nonylphenol has been referred to in the list of priority substances in the Water Frame Directive and in the 3rd draft Working Document on Sludge of the EU. Consequently there is currently a concern within some industries about the possibility of future regulations that may impose the removal of trace contaminants from contaminated effluents. The significance of upgrading sewage treatment works with advanced treatment technologies for removal of trace contaminants is discussed.     

Resourceful Utilization of Tannery Wastewater

Leather industry is an important light industry in China.Leather making requires a series of chemical treatment.Degreasing,unhairing and chrome tanning wastewaters are the main portions of tannery wastewater.Reclaiming and reusing these wastewaters can eliminate 80% of COD,75% of BOD,95% of chromium and 93% of sulfuret,furthermore reduce environment impact,decrease treatment costs,save chemicals and water.Some application methods of wastewater reclamation and reuse for different operations were reported.The suitable reclamation and reuse technologies can enable leather making processes more rational,and realize the recovery and recycle of several chemicals in the tannery.Resourceful utilization of tannery wastewater should mate with renovating production technology,updating equipment,and must be guaranteed sufficiently by environmental protection measures.     

Inhibition of microbial activity of activated sludge by ammonia in leachate

Leachate samples were collected from the West New Territory Landfill (WENT), Hong Kong, and characterized in the laboratory. The analytical results confirmed that it has a typical nature of aged leachate with a low BOD₅/COD ratio of 0.22 and a high strength of ammonia-nitrogen around 5 g/L. A lab-scale study was conducted to investigate the inhibition of microbial activity of the activated sludge. In the first test, glucose-based synthetic wastewater was used in two parallel reactors. The experimental results demonstrated that COD removal declined from 95.1 to 79.1% and the dehydrogenase activity of the sludge decreased from 11.04 to 4.22 μg TF/mg mixed liquor suspended solids (MLSS), when the ammonia-nitrogen concentration increased from 50 mg/L to 800 mg/L progressively. The remaining NH₃⁺-N residue in the treated wastewater increased from 0.58 mg/L to 649 mg/L extensively. In the second test, mixed wastewater samples containing glucose and raw leachate were fed into six parallel biological reactors and operated on batch mode. The experimental results showed COD removal decreased from 97.7 to 78.1% and the dehydrogenase activity decreased from 9.29 to 4.93 μg triphenyl formazon (TF)/mg MLSS, respectively, when the ammonia-nitrogen concentration increased within the same range. Microbial inhibition could also be substantiated by a decrease of specific oxygen uptake rate (SOUR) from 68 to 45 mg O₂/g MLSS. These results suggested leachate containing high-strength ammonia-nitrogen should be pretreated to an acceptable NH₄⁺-N level before it is fed into biological reactors.     

Perfluoroalkyl compounds in Danish wastewater treatment plants and aquatic environments

This study reports the results of a screening survey of perfluoroalkyl compounds (PFCs) in the Danish environment. The study included point sources (municipal and industrial wastewater treatment plants and landfill sites) and the marine and freshwater environments. Effluent and influent water and sewage sludge were analysed for point sources. Sediment, blue mussels (Mytilus edulis) and liver from plaice (Pleuronectes platessa), flounder (Platichthys flesus) and eel (Anguilla anguilla) were analysed for the freshwater and marine environments. The results obtained show a diffuse PFCs contamination of the Danish environment with concentrations similar to those measured in other countries with the absence of primary contamination sources such as fluorochemical production. PFOS and PFOA were generally the most dominating PFCs measured in both point sources and the aquatic environments. PFCs were found in both inflow and outflow water and sewage sludge from municipal and industrial wastewater treatment plants (WWTPs), indicating that WWTPs can be significant sources to PFCs in the environment. This is also reflected in the locally elevated PFCs concentrations found in fish like eels from shallow freshwater and marine areas. However, the highest PFCs concentrations found in fish in this study was in plaice from the Skagerrak (156 ng/g wet weight PFOS), but it is unknown if this can be related to significant sources in the North Sea region or to differences between species. The concentrations of PFCs were below the detection limit in all analysed freshwater and marine samples of sediment and mussels. Despite the relatively low PFCs concentrations measured in marine fish, the high bioaccumulation potential of PFCs, particularly PFOS, may lead to high concentrations of PFCs in marine mammals as shown by previous investigations.     

Resourceful Utilization of Tannery Wastewater

Abstract

Leather industry is an important light industry in China. Leather making requires a series of chemical treatment. Degreasing, unhairing and chrome tanning wastewaters are the main portions of tannery wastewater. Reclaiming and reusing these wastewaters can eliminate 80% of COD, 75% of BOD, 95% of chromium and 93% of sulfuret, furthermore reduce environment impact, decrease treatment costs, save chemicals and water. Some application methods of wastewater reclamation and reuse for different operations were reported. The suitable reclamation and reuse technologies can enable leather making processes more rational, and realize the recovery and recycle of several chemicals in the tannery. Resourceful utilization of tannery wastewater should mate with renovating production technology, updating equipment, and must be guaranteed sufficiently by environmental protection measures.     

Parameters affecting biological phosphate removal from wastewaters

This paper reviews some of the key wastewater composition parameters, which influence the biological removal of phosphate from wastewaters, such as COD content, volatile fatty acid (VFA) content, cation concentration, phosphorus load, pH and food to microorganism ratio. The discussion also focuses on operational parameters affecting successful nutrient removal in wastewater treatment plants, such as temperature, sludge quality, sludge settlement, dissolved oxygen (DO) concentration, anaerobic P-release and secondary P-release. The aim of this review is to compile an updated document for researchers and operators of biological nutrient removal (BNR) systems. In addition, the article will provide a good foundation for readers with no prior knowledge of the process.     

Treatment of sugar industry wastewater using a combination of thermal and electrocoagulation processes

Sugar industries require a large amount of water for processing, and also generate large amounts of high-degree polluted wastewater. To maintain the water balance in the industry, it is imperative that effective treatment methods need to be devised to treat the wastewaters. The main aim of the present work is to treat the sugar industry wastewater by combined thermal and electro-oxidation methods with a metal and a catalyst based on ferrous material. Results showed a reduction of 75.6% of COD and 79.2% of colour content with thermal treatment, and 97.8% of COD and 99.7% of colour with combined thermal and electrocoagulation treatments under optimum conditions. These reduction levels are adequate for recycling limits.     

Development of extraction method of pharmaceuticals and their occurrences found in Japanese wastewater treatment plants

In this study, occurrence of 66 PPCPs (pharmaceuticals and personal care products) in liquid and solid phases of sewage sludge was elucidated. The extraction methods for the PPCPs from sludge were newly developed employing Pressurized Liquid Extraction (PLE) and Ultrasonic Solvent Extraction (USE). As an appropriate method, PLE using water (pH2), PLE using methanol (pH4), and USE using mixture of methanol and water (1/9,v/v, pH11) was found most effective because total recovery of most of the PPCPs indicated 40 to 130%. The developed extraction method with previously developed method for liquid phase analysis was applied to field survey at wastewater treatment plants (WWTPs) in Japan. 56 compounds were detected from the primary sludge and 61 compounds were detected from the excess sludge. The concentration was ranged between several ng/g and several μg/g. Solid-water distribution coefficient (Log K_d) ranged between 0.9 L/kg (Caffeine) and 3.7 L/kg (Levofloxacin) for primary sludge and between 1.4 L/kg (Sulpirid) and 4.3 L/kg (Mefenamic acid) for excess sludge.     

环境税对高污染行业的影响研究——以湖南邵阳高COD排放行业为例

针对开征环境税对高污染行业的影响,选取湖南省邵阳市为研究区域,以COD排放为例,选择了COD排放量最多的造纸及纸制品业、农副食品加工业、化学原料和化学制品制造业,调查各行业的废水治理成本。通过调查发现行业平均治理成本差别较大,从1.55元/kg到8.11元/kg,调查时点区域排污费收费标准0.7元/kg,相比行业平均治理成本太低,就几乎不具有激励减排的功能,同时也不具备筹集环境治理资金的功能。通过分析湖南邵阳高COD排放行业征收环境税的影响发现,无论基于行业废水平均治理成本制定环境保护税税率,还是考虑边际治理成本提高的情况下制定环境保护税税率,对行业大部分企业利税影响率均小于5%。而且基于行业治理成本征税,有利于淘汰行业中高污染的落后产能,促进行业整体资源优化配置,从长远来看有利于整个行业的发展,对于推动供给侧改革,改善环境质量具有重要意义。 关键词： 环境税;影响分析;高污染行业;供给侧改革     

中国经济发展与水环境压力脱钩态势评价与展望

在对经济发展的水环境压力概念进行合理界定基础上,建立经济发展与水环境压力的脱钩指标体系。通过国内外相关文献研究与数据收集,构建了中国经济发展与水环境压力的脱钩潜力评价与时态分析模型,评价1986~2010年水利发展不同阶段中国经济总量增长与废水排放的脱钩潜力与脱钩时态、以及经济总量增长与工业废水化学需氧量的脱钩时态。在此基础上,根据水环境库茨涅茨曲线变化趋势,对我国废水排放总量的自然发展趋势进行预测,并根据国家发展规划对废水排放总量预测结果进行修正。同时,结合国家发展规划和环境保护规划,对水环境压力脱钩进行展望。结果表明,我国经济发展与废水排放总量总体处于弱脱钩发展态势、与工业废水化学需氧量排放总量总体处于强脱钩发展态势。预计2020年左右,我国经济发展与水环境压力有望保持绝对脱钩的发展态势,水环境得到彻底改善与净化     

Current status of urban wastewater treatment plants in China

The study reported and analyzed the current state of wastewater treatment plants (WWTPs) in urban China from the perspective of treatment technologies, pollutant removals, operating load and effluent discharge standards. By the end of 2013, 3508 WWTPs have been built in 31 provinces and cities in China with a total treatment capacity of 1.48 × 10⁸ m³/d. The uneven population distribution between China's east and west regions has resulted in notably different economic development outcomes. The technologies mostly used in WWTPs are AAO and oxidation ditch, which account for over 50% of the existing WWTPs. According to statistics, the efficiencies of COD and NH₃–N removal are good in 656 WWTPs in 70 cities. The overall average COD removal is over 88% with few regional differences. The average removal efficiency of NH₃–N is up to 80%. Large differences exist between the operating loads applied in different WWTPs. The average operating loading rate is approximately 83%, and 52% of WWTPs operate at loadings of < 80%, treating up to 40% of the wastewater generated. The implementation of discharge standards has been low. Approximately 28% of WWTPs that achieved the Grade I-A Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918–2002) were constructed after 2010. The sludge treatment and recycling rates are only 25%, and approximately 15% of wastewater is inefficiently treated. Approximately 60% of WWTPs have capacities of 1 × 10⁴ m³/d–5 × 10⁴ m³/d. Relatively high energy consumption is required for small-scale processing, and the utilization rate of recycled wastewater is low. The challenges of WWTPs are discussed with the aim of developing rational criteria and appropriate technologies for water recycling. Suggestions regarding potential technical and administrative measures are provided.     

Sulfide production during anaerobic lagoon treatment of tapioca wastewater

Laboratory-scale experiments on anaerobic lagoon treatment of tapioca wastewater were conducted under ambient, tropical conditions. The objectives of this study were to investigate factors that affect hydrogen sulfide production and to propose means to control the formation of hydrogen sulfide in lagoon effluents. The concentrations of sulfides were found to increase with increasing organic loading from 2.76 to 5.77 kg COD/m³.d, decreasing hydraulic retention time; and increasing pH from 3 to 7. The maximum total sulfide concentration of 18.8 mg/L occurred at the organic loading of 5.77 kg COD/ m³.d and neutral pH. the maximum H₂S concentration was calculated to be 13.3 mg/L which occurred in the laggoon operated at an organic loading of 5.77 kg COD/m³.d and a pH of 5. The control of odour problems due to the H₂S formation should be possible by raising pH of the lagoon water to be more than 8 or operating the lagoon at low organic loadings.     

Effect of ozone pre-treatment on sludge production of aerobic digestion processes

The effect of ozone in a chemical sludge disintegration process was evaluated. Sludge solution chemical oxygen demand (COD), total suspended solids (TSS) and settling were investigated in single and sequential processes. A significant influence of ozone dose on sludge disintegration was observed: ozone was utilised to degrade the soluble organic matter and to destroy cell surfaces and release the cell liquids. For a single ozonation step, we found an optimum ozone dose in the range of 0.008–0.013 g O₃/g TSS to give the best COD and TSS removal efficiency. Disintegrated sludge was treated in a sequential process consisting of consecutive ozonation and bio-aeration (i.e. O₃ + biological treatment). The tendency was dependent on accumulated ozone, treatment time and operational conditions. An accumulated ozone dose of 0.055 g O₃/g TSS in two separate ozonation processes followed by biological treatments led to COD and TSS removal efficiency of 53 and 46.6%, respectively. The removal efficiency was improved by increasing aerobic treatment time and/or by mixing ozonated sludge with non-ozonated sludge. The settling ability of sludge was found to be fast at very low specific ozone doses. An observed tendency was the effect of ozone on cell disintegration and protein liberation. The use of sequential processes improved the settling tendency of sludge.