Secondary effluent reclamation: combination of pre-treatment and disinfection technologies.

A study was carried out to evaluate the efficiency of secondary effluent additional treatment, using a combination of pre-treatments (ring filter, physico-chemical and infiltration-percolation) followed by disinfection methods (chlorine dioxide, peracetic acid and ultraviolet light). Three different indicator microorganisms were determined: E. coli, total coliforms and somatic bacteriophages. The results show better efficiency of physico-chemical and infiltration-percolation processes. Bacteriophages were eliminated to a lesser extent than bacterial indicators in all the treatment systems. Chlorine dioxide and peracetic acid seems to be more efficient in disinfection than ultraviolet light when a ring filter is the pre-treatment used. For the same doses and contact times, the efficiency of the disinfection methods is higher when the pre-treatment used is the physico-chemical or the infiltration-percolation system. The final effluent quality from the physico-chemical treatment train and the infiltration-percolation treatment train, followed by the disinfectants, achieves an E. coli content that allows the reuse in most of the uses described in the Spanish legislation for wastewater reuse.     

Comparison of SAR (sodium adsorption ratio) between RO and NF processes for the reclamation of secondary effluent.

Secondary effluent reclamation and reuse has been considered as an alternative for agricultural irrigation water. Whilst all constituents in the reclaimed wastewater could affect plant growth and soil characteristics, the most important parameters for agricultural irrigation are salinity and SAR (Sodium Adsorption Ratio). Salinity affects the availability of crop water and sodium causes clay soils to disperse. Membrane technologies, especially NF (Nano-Filtration) and RO (Reverse Osmosis), have played in a key role reclaiming the secondary effluent. RO can remove monovalent and divalent cations simultaneously. However NF processes reject preferably divalent cations and most monovalent ions are allowed to pass through the NF membranes. This could make them have different SAR values for both NF and RO processes. Therefore the primary objective of this study is to examine if the SAR values of the reclaimed water could be changed while they undergo NF and RO processes. The measured SAR values of the secondary effluent, NF permeate, and RO permeate were 1.78, 4.67, and 0.72 respectively. The SAR value after NF (4.67) increased to more than twice that of the feed solution, whereas the SAR of the RO permeate decreased to 0.72. In general, the higher SAR the water has, the greater risk the soils have. Although the SAR value after NF was within the safe range, this increased SAR value will affect permeability of soil, thus limiting the reclaimed wastewater use for as agricultural irrigation water. Consequently, when the NF system is used for the reclamation of the secondary effluent, SAR has to be examined first because potentially it tends to increase the SAR value.     

Dissolved oxygen, COD, nitrogen and phosphorus profiles in a continuous sand filter used for WWTP effluent reclamation

Continuous sand filtration (CSF) offers interesting potential for the extensive treatment of wastewater treatment plant (WWTP) effluents for water reclamation and/or restrictive discharge. Research on concentration profiles over the height of the CSF shows that most bacteriological conversions are restricted to the lower part of the filter bed. Dissolved oxygen (DO) rapidly decreases to below 1 mg/L in the first 0.4 m of the filter bed, applying hydraulic velocities of 12.9 ～ 14.9 m/h and 10 ～ 20 mm/min sand velocities, independent of the methanol dosage. The DO decrease agrees with the observed decrease in chemical oxygen demand (COD). At the given operational conditions, NO(x)-N and N-total removal is dedicated to the first 0.9 m of the filter bed. Results show that by optimising the CSF operational conditions the very restrictive effluent N and P values of 2.2 and 0.15 mg/L, respectively, as described in the European Water Framework Directive, can be met.     

Development of an integrated membrane process for water reclamation.

An integrated membrane process (IMP) comprising a membrane bioreactor (MBR) and a reverse osmosis (RO) process was developed for water reclamation. Wastewater was treated by an MBR operated at a sludge retention time (SRT) of 20 days and a hydraulic retention time (HRT) of 5.5 h. The IMP had an overall recovery efficiency of 80%. A unique feature of the IMP was the recycling of a fraction of RO concentrate back to the MBR. Experimental results revealed that a portion of the slow- and hard-to-degrade organic constituents in the recycle stream could be degraded by an acclimated biomass leading to an improved MBR treatment efficiency. Although recycling concentrated constituents could impose an inhibitory effect on the biomass and suppress their respiratory activities, results obtained suggested that operating MBR (in the novel IMP) at an F/M ratio below 0.03 g TOC/g VSS.day could yield an effluent quality comparable to that achievable without concentrate recycling. It is noted in this study that the novel IMP could achieve an average overall TOC removal efficiency of 88.940% and it consistently produced product water usable for high value reuse applications.     

Application of an anaerobic hybrid reactor for petrochemical effluent treatment

An anaerobic hybrid reactor (UASB/Filter) was used for petrochemical wastewater treatment in mesophilic conditions. The seeded flocculent sludge from a UASB plant treating dairy wastewater, acclimatized to the petrochemical wastes in a two-stage operation. After start up, under steady-state conditions, experiments were conducted at OLRs of between 0.5 and 24 kg TCOD m(-3) d(-1), hydraulic retention times (HRT) of 4-48 h and up-flow velocities 0.021-0.25 mh(-1). Removal efficiencies in the range of 42-86% were achieved at feed TCOD concentrations of 1,000-4,000 mg L(-1). The results of reactor performance at different operational conditions and its relations are presented and discussed in this paper. Then, the obtained data are used for determination of kinetic models. The results showed that a second-order model and a modified Stover-Kincannon model were the most appropriate models for this reactor. Finally, the biogas production data were used for the determination of biogas production kinetics.     

城市污水再生利用现状分析

概述了我国城市供水状况和用水结构,指出了水资源短缺引起的各种供水问题的严重性,探讨了进行污水再生利用,推进污水资源化的重大意义。详细分析了国内外污水再生利用的发展情况,包括工艺流程、设施(设备)能力、实际利用量、存在问题及原因分析、技术经济效益等内容,并结合工程实践经验提出了相应的建议。     

Recycling of treated domestic effluent from an on-site wastewater treatment system for hydroponics.

An alternative method to conserve water and produce crops in arid regions is through hydroponics. Application of treated wastewater for hydroponics will help in stripping off nutrients from wastewater, maximising reuse through reduced evaporation losses, increasing control on quality of water and reducing risk of pathogen contamination. This study focuses on the efficiency of treated wastewater from an on-site aerobic wastewater treatment unit. The experiment aimed to investigate 1) nutrient reduction 2) microbial reduction and 3) growth rate of plants fed on wastewater compared to a commercial hydroponics medium. The study revealed that the chemical and microbial quality of wastewater after hydroponics was safe and satisfactory for irrigation and plant growth rate in wastewater hydroponics was similar to those grown in a commercial medium.     

Treatment of paper mill effluent using an anaerobic/aerobic hybrid side-stream membrane bioreactor

This paper presents the design and operational performance data of an anaerobic/aerobic hybrid side-stream Membrane Bioreactor (MBR) process for treating paper mill effluent operated over a 6 month period. The paper mill effluent stream was characterized by a chemical oxygen demand (COD) range of between 1,600 and 4,400 mg/L and an average BOD of 2,400 mg/L. Despite large fluctuations in COD feed concentration, stable process performance was achieved. The anaerobic Expanded Granular Sludge Bed (EGSB) pre-treatment step effectively lowered the organic loading by 65 to 85%, thus lowering the MBR COD feed concentration to consistently below 750 mg/L. The overall MBR COD removal was consistent at an average of 96%, regardless of the effluent COD or changes in the hydraulic retention time (HRT) and organic loading rate (OLR). Combining a high-rate anaerobic pre-treatment EGSB with a Modified Ludzack-Ettinger (MLE) MBR process configuration produced a high quality permeate. Preliminary NF and RO results indicated an overall COD removal of around 97 and 98%, respectively.     

浙江省滩涂围垦发展综述

浙江省滩涂资源丰富，围垦历史悠久，是围垦实践中，创造了许多新技术，积累了丰富经验，取得了丰硕成果，滩涂围垦是实现我省耕地占补平衡和耕地总量动态平衡的有效途径之一，总结了围垦技术进步对围垦事业发展的影响，根据我省滩涂围垦总体规划和围垦工程技术发展的方向，提出了今后围垦发展的趋势。     

Membrane bioreactors for water reclamation.

Singapore has been using dual membrane technology (MF/UF RO) to produce high-grade water (NEWater) from secondary treated sewage. Membrane bioreactor (MBR) has very high potential and will lead to the further improvement of the productivity and quality of high-grade water. This study was focused on the technical feasibility of MBR system for water reclamation in Singapore, making a comparison between various membrane systems available and to get operational experience in terms of membrane cleaning and other issues. Three MBR plants were built at Bedok Water Reclamation Plant with a design flow of 300 m3/day each. They were commissioned in March 2003. Three different types of submerged membranes were tested. They are Membrane A, plate sheet membrane with pore size of 0.4 microm; Membrane B, hollow fibre membrane with pore size of 0.4 microm; and Membrane C, hollow fibre membrane with pore size of 0.035 microm. The permeate quality of all the three MBR Systems were found equivalent to or better than that of the conventional tertiary treatment by ultrafiltration. MBR permeate TOC was about 2 mg/l lower than UF permeate TOC. GC-MS, GC-ECD and HPLC scan results show that trace organic contaminants in MBR permeate and UF permeate were in the same range. MBR power consumption can be less than 1 kwh/m3. Gel layer or dynamic membrane generated on the submerged membrane surface played an important role for the lower MBR permeate TOC than the supernatant TOC in the membrane tank. Intensive chemical cleaning can temporarily remove this layer. During normal operation conditions, the formation of dynamic membrane may need one day to obtain the steady low TOC levels in MBR permeate.     

Optimal performance of an immersed membrane bioreactor equipped with a draft tube for domestic wastewater reclamation.

One of the options to prevent membrane fouling is to implement air lifting that can improve the cake removal from the membrane surface. This study presents the results of tests that were carried out at the Institutes for Desert Research, Kiryat Sde-Boker, Israel, and focused on the influence of hydrodynamic conditions on fouling in a pilot-scale immersed membrane bioreactor (IMBR) using a hollow fiber membrane module of ZW-10 (Zenon Environmental, Canada) under ambient conditions. In this system, the cross-flow velocities across the membrane surface were induced by one conical and four cylindrical draft-tubes. The relationship between the crossflow velocity and the aeration intensity, the influence of the crossflow on fouling rate under various hydrodynamic conditions were investigated and optimal operating conditions were obtained. Optimal operating conditions were reached during the long-term experiment period (70 days) for the treatment of domestic wastewater. The system was stable without external chemical cleaning. The results showed that the permeate was of high quality, and the removal of COD and BOD was 94.0% and 98.8%, respectively.The crossflow near the membrane surface reveals a major contribution for minimizing membrane fouling, and could offer guidelines for future design of similar systems.     

Filtration characteristics of immersed coarse pore filters in an activated sludge system for domestic wastewater reclamation.

The filtration characteristics of two different module configurations with coarse pore filter (non-woven fabric) were investigated for sludge floc separation in an activated sludge reactor for domestic wastewater reclamation. A polypropylene non-woven fabric filter (35 g/m2) was used for the two different module configurations, one flat and one tubular type, each with a filtration area of 0.052 m2. The different module types, submerged in the oxic compartment of A/O (anaerobic/oxic) type reactors, were operated simultaneously. The filtration fluxes were gradually increased from 0.5 to 1.2 and 1.73 m/d. The filtration pressures were more stably maintained for the tubular type module than the plate type. The tubular type module installed horizontally with two-side suction showed less filtration pressures than the tubular type module installed vertically with one-side suction. The solid separation was significantly high showing less than 5 mg/L effluent solids. The organic and T-N removal efficiencies were around 95 and 50%, respectively. The 85% removal of T-P was achieved with 20 mg/L injection of PAC (poly-aluminum chloride).     

Concept of an innovative water management system with decentralized water reclamation and cascading material-cycle for agricultural areas

Unlike in urban areas where intensive water reclamation systems are available, development of decentralized technologies and systems is required for water use to be sustainable in agricultural areas. To overcome various water quality issues in those areas, a research project entitled 'Development of an innovative water management system with decentralized water reclamation and cascading material-cycle for agricultural areas under the consideration of climate change' was launched in 2009. This paper introduces the concept of this research and provides detailed information on each of its research areas: (1) development of a diffuse agricultural pollution control technology using catch crops; (2) development of a decentralized differentiable treatment system for livestock and human excreta; and (3) development of a cascading material-cycle system for water pollution control and value-added production. The author also emphasizes that the innovative water management system for agricultural areas should incorporate a strategy for the voluntary collection of bio-resources.     

Treatment of an ECF effluent by combined use of activated sludge and advanced oxidation process.

The combined biological and chemical treatments of the cellulose effluents have been studied aiming to promote a more significant degradation of their recalcitrant compounds and to reduce their toxicity, as compared with the isolated treatments. In this work the effluent from acid stages of the ECF bleaching of Eucalyptus urograndis pulp was treated by using separately activated sludge and UV radiation and its combination. The treatment efficiency was evaluated by colour, total phenol, COD, BOD, UV spectroscopy, molar weight distribution and toxicity. The untreated effluent presented 587 +/- 18 CU, 19.3 +/- 0.6 mg.L(-1) of total phenol, 2246 +/- 137 mgO2.L(-1) of COD and 904 +/- 48 mgO2.L(-1) of BOD. It did not show acute toxicity to Escherichia coli, but presented chronic toxicity to Selenastrum capricornutum (EC50 = 25%). The sludge treatment resulted in a colour increasing of 42% and decreasing of total phenol, COD and BOD of 33%, 64% and 92%, respectively. The UV radiation treatment for 120 min resulted in a decrease of colour, total phenol, BOD and COD of 70%, 43%, 62% and 43%, respectively. The combined treatment promoted an expressive decrease for colour and total phenol. The UV absorption indicated a degradation of the aromatic compounds. The biological treatment did not remove chronic toxicity and after UV radiation treatment, a 10 times improving toxicity was noticed.     

荆江大堤加固工程中的长排距吹填施工

针对荆州市长江干堤特别是荆江大堤历史遗留的险工险段出现的管涌险情处理,采用了长排距吹填施工技术.为此,对原有200 m3/h绞吸式挖泥船进行了改造,配以接力泵站,采用了"一船两站"的施工方案.延长输泥排距15 km,解决了荆江堤防加固及防洪工程中的一些险工险段因土源缺乏而无法施工的难题.从而保证了大堤在防洪减灾中发挥了较好的作用.     

黑龙江垦区冲刷沟治理措施

分析了黑龙江垦区冲刷沟成因、特点及危害,并提出相应的治理措施。     

萧围北线低滩治江围涂工程设计与施工

萧围北线低滩治江围涂工程位于钱塘江下游河口附近,滩涂高程低,处于涌潮与山洪易顶冲的凹岸,施工难度较大,工程建设采用先抛筑石丁坝、顺坝促淤、边促淤边围堤的总体设计方案,并在施工过程中,调整设计方案,加快工程进度,节约投资,效果显著.     

温州浅滩试验堤软基处理的几点启示

温州浅滩工程地质软基深厚,工程规模大,软基处理难度高,为优选工程方案,通过试验堤工程来研究采用塑料排水板、土工材料的复合加固法,并结合分层间歇加荷压载和监测手段,妥善地解决了在高含水量深厚软基上建造堤坝的稳定控制问题.     

围垦工程中围堤技术研究思路探讨

从分析浙江省围堤技术现状着手,对当前围堤技术主要存在的问题如地基处理技术相对单一、传统土石结构对环境的影响大、闭气土方快速脱水固结技木尚未获根本突破、施工技术含量偏低等进行了简评,并提出了围堤结构多功能、围涂与湿地保护兼顾、跨行业技术应用、快速筑堤技术等方面进一步的研究思路。