污水处理-英文文献4

Desalination 231 (2008) 20–260011-9164/08/$– See front matter © 2008 Elsevier B.V. All rights reservedat The 4th IWA Conference on Membranes for Water and Wastewater TreatmentMay 15–17, 2007, Harrogate, UK*Corresponding author.Upgrading and retrofitting of municipal wastewater treatmentplants by means of membrane bioreactor (MBR) technologyCh. Brepols a , E. Dorgeloh b , F.-B. Frechen c , W. Fuchs d , S. Haider e , A. Joss f ,K. de Korte g , Ch. Ruiken g , W. Schier c *, H. van der Roest h , M. Wett i , Th. Wozniak jaErftverband, Bergheim, GermanybPrüf- und Entwicklungsinstitut für Abwassertechnik (PIA) an der RWTH Aachen, Germany cDepartment of Sanitary and Environmental Engineering - DESEE, University of Kassel, Germany Tel. +49 (561) 8043817; Fax +49 (561) 8043642; email: wernfried.schier@uni-kassel.de dUniversity of Natural Resources and Applied Life Sciences – Vienna, Department IF A-Tulln,Institute for Environmental Biotechnology, Tulln, AustriaeH2Office Abwassertechnik, Wien, AustriafEAWAG — Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, SwitzerlandgDWR — Dienst Waterbeheer en Riolering, Amsterdam, The Netherlands hDHV —Consultancy and Engineering, Amersfoort, The Netherlands iSüddeutsche Abwasserreinigungs-Ingenieur GmbH, Ulm, Germanyjwws consulting, Reutlingen, GermanyReceived 17 May 2007; accepted revised 20 November 2007AbstractIn the future, upgrading of existing wastewater treatment plants (wwtps) will become the more challenging task than erection of wholly new plants, as most of the plants (e.g. necessary in Germany) do exist already. Since some time, MBR technology has been taken into consideration and has been realised as an alternative for wwtp upgrading.This paper gives an overview about some relevant preconditions, basic upgrading concepts and examples of already upgraded wwtps using MBR technology.Keywords: Municipal wastewater treatment; Upgrading; MBR technologydoi:10.1016/j.desal.2007.11.035Ch. Brepols et al. / Desalination 231 (2008) 20–26211. IntroductionMany wwtps suffer from an inadequate level of treatment provided. There are several reasons for the need of retrofitted and/or upgraded equip-ment, such as expiry of lifespan, the increase of wastewater flow or load or higher treatment stan-dards due to a change of legal framework. In gen-eral, no standard solutions for the upgrading of wastewater treatment systems are available and the transfer of a certain measure from one case to another is limited. In fact, the optimum answer in each individual case is largely site-dependent. Accordingly, there is a broad spectrum of mea-sures that might be employed. In most cases it is not a singular action to be taken, but the upgrad-ing will incorporate a set of different interlocking components both at the drainage system and the wastewater treatment plant.The MBR process is an emerging advanced wastewater treatment technology that has been successfully applied at an ever increasing num-ber of locations around the world. It involves a suspended growth activated sludge system that utilizes microporous membranes for solid/liquid separation as a substitute of the conventional sec-ondary clarifier. MBR technology has not only attracted increasing interest for the set up of new wastewater treatment systems but also it has high potential looking at upgrading tasks of already existing wwtps.2. Considerations for the choice of MBR technologySince membrane filtration allows raised sludge concentrations, the activated sludge tank volume can be significantly reduced. In combination with the option to convert the secondary clarifier, that is no longer required as a sedimentation tank, as an additional activated sludge tank, the treatment capacity of the existing plant can be largely ex-tended. That way it is possible to upgrade exist-ing wwtps from simple carbon removal to BNR systems just using the already existing volume.Therefore favourable conditions for the choice of MBR technology are given, where retrofitting of the existing plant by the conventional activated sludge (CAS) process would demand for substan-tial extension of the activated sludge volume. As well, where limitations due to insufficient effi-ciency of the secondary clarification basin exist, particularly however, where both problems have to be solved.MBR technology should also be considered if high effluent criteria such as removal of suspended solids or absence of pathogens have to be met. Examples are discharge into small creaks as well as into bathing water or other sensitive areas.Due to the small space requirement the MBR offers special advantages if the given location holds no or only a limited amount of area in re-serve. Moreover, the small footprint allows a com-plete indoor installation in a building designed to blend in with its surrounding environment and such to address issues of visual amenity, odour or noise.Another distinct advantage of MBR technol-ogy is direct utilisation of the effluent for reuse purposes. The water reuse potential includes irri-gation of agricultural land, recharge of aquifers or river flow replenishment. On several occasions this was the major decision criteria to opt for MBR technology.With the choice of the MBR special attention should be paid to the fact that the investment costs are largely correlated with the hydraulic peak flow. This parameter determines the total membrane surface area which needs to be installed. There-fore, accompanying measures to minimize wet weather flow or to harmonise resultant wastewa-ter largely contribute to cost effectiveness of the MBR approach. One option for dealing with high wet weather peaks is to use the former secondary clarifier as storage volume. Another option is hy-brid systems where the conventional system is used as a backup to treat the inflow volume that exceeds the hydraulic membrane capacity. An al-ready realised hybrid concept designs the MBR22Ch. Brepols et al. / Desalination 231 (2008) 20–26line to treat the dry weather flow at the maximum.The inflow volume beyond dry weather condi-tions is treated conventionally.3. Modification of the operation mode using the MBR approachWith the change of sludge/treated wastewater separation from gravity settling to membrane fil-tration the following process configurations are available:3.1. MBR with or without a separate filtration chamberWith upgrading of wwtp as a pure MBR pro-cess the question is to be cleared whether exist-A: substitution of the sedimentation tank by a separate filtration chamberB: sedimentation tank: change of utilisation as biological volumeC: change of flow scheme and immersed membranes within the biologyinitial Fig. 1. Upgrading variations using MBR technology.ing sedimentation tanks can be included sensibly in the future concept of utilisation. According to the structural state it can be possible to use these tanks as an additional biological volume. Also the suitable installation and operation of the mem-brane modules either in activated sludge tanks or in separated filtration chambers depends on the quality of the respective structural situation. At this point wide engineering space is given. Fig. 1shows some possible variations.3.2. Hybrid systemsThe combination of the CAS process and the MBR process is understood as the hybrid proce-dure. Fig. 2 shows two basic operation concepts of hybrid processes (among other hybrid systems).Ch. Brepols et al. / Desalination 231 (2008) 20–2623Besides, a fullness of mixing variations is pos-sible. The flow concept of the sludge streams be-tween both biological units at parallel operation mode or serial operation mode can be operated separately or combined according to the local cir-cumstances (grey arrows in Fig. 2). In the latter case possible differences are to be taken into con-sideration concerning the sludge qualities, in par-ticular, the quality of sedimentation and the MLSS concentrations.3.3. Other processesBeside the combination with the CAS process also combinations with other wastewater treat-ment procedures are possible, e.g. with SBR tech-nology [1] or with pond technology. Today SBR technology integrating membrane technology as separation process is used at industrial applica-tions or at package plants. Applications combin-ing pond technology and MBR technology are op-parallelserialFig. 2. Basic operation concepts of the hybrid procedure.erated at wwtp St. Peter ob Judenburg, Austria and at wwtp Ihn, Germany.3.4. MBR process with low MLSS concentration In cases when available sedimentation volume is used as additional biological volume, the amount of total biological volume increases to a degree, that clearly exceeds the usual volume de-mand of a conventional MBR process with ap-propriate MLSS concentrations ranging from 10kg/m³ to 15 kg/m³. Dimensioning the MLSS concentration both the available biological vol-ume and the guarantee of the aerobic SRT have to be taken into consideration. Usually this dimen-sioning ends up with less MLSS concentration in the range of 5–7 kg/m³ [2,3] compared with con-ventional MBR operating circumstances. If such a draught can be realised, the usual disadvantages (sensibility compared to impact load, reduced al-pha value) could be overcome by MBR process24Ch. Brepols et al. / Desalination 231 (2008) 20–26to a great extent. Beside the anyway raised efflu-ent quality other advantages of this upgrading concept can be named:•considerable biological reserve capacities for future extension;•smaller place consumption compared to a con-ventional upgrading concept.Some manufacturers of membrane modules recommend not falling short of a given MLSS concentration directly at the membrane or within a separated filtration chamber. Thus, the suitabil-ity of the respective membrane modules for the “low MLSS operation mode” is to be clarified. Nevertheless, by the construction of a separate filtration chamber optimal MLSS concentrations at the membrane and within the biological zone can be adapted accordingly.3.5. MBR in combination with anaerobic sludge stabilizationUp to now most municipal MBR plants are dimensioned with aerobic simultaneous sludge stabilization. In principle the MBR process also can be combined with anaerobic sludge stabiliza-tion. Some single studies assume dependence be-tween increasing fouling potential and increasing F/M-ratio or rather decreasing SRT [4–6]. A final statement cannot be met yet. If the MBR process is dimensioned with a short SRT, hence, possible intensified fouling effects have to be considered.If the MBR process is dimensioned with a long SRT, slightly reduced digester gas production can be expected. A possible process variation features the digestion of only primary sludge. Thus, in an upgrading situation the cost intensive new build-ing of digestion volume can be avoided.4. Experiences from full-scale applicationsThe full version of DWA WG KA-7.4 report includes all subsequently mentioned wwtps:•wwtp St. Peter ob Judenburg, Austria •wwtp Schilde, Belgium •wwtp Eitorf, Germany•wwtp Bergheim-Glessen, Germany•wwtp Brescia, Italy•wwtp Viareggio, Italy•wwtp Heenvliet, Netherlands•wwtp Rietliau, SwitzerlandUpgrading of wwtps by means of MBR tech-nology is not a question of special membrane types. The above mentioned plants are equipped with usual and well known hollow fibre mem-branes as well as with flat sheet membranes.In the following two plants out of the above mentioned are now introduced more detailed. Besides, the German wwtp Bergheim-Glessen is an example for a complete process rearrangement. The Swiss wwtp Rietliau shows a hybrid solu-tion.4.1. wwtp Bergheim-Glessen, GermanyIn the case of the wwtp Bergheim-Glessen MBR technology is used to meet advanced re-quirements caused by the discharge of wastewa-ter to sensitive wetland. Upgrading occurs at the existing location using extensively already exist-ing constructions. Treatment efficiency will be rapidly increased by introducing MBR technol-ogy. Hence, in addition, the wastewater of a neighbouring, smaller wwtp, likewise in the need of upgrading, is led across, treated and afterwards led back. Thus, the wwtp load is raised from 5,000p.e. nowadays to 9,000 p.e. Wastewater quantity to be treated from now on amounts to 900,000 m³/a. Fig. 3 illustrates the flow diagram.The mechanical pre-treatment is completely renewed consisting of three units: screening (gap size 6 mm), aerated grit chamber and grease trap, sieving (mesh geometry, gap size 1 mm). The existing oxidation ditch furthermore will be used as activated sludge volume. SRT should amount about 25 d, MLSS concentration is dimensioned with only 8 kg/m³. In time of maximum inflow HRT amounts to 6 h. The membrane modules are installed in four separated filtration chambers.Ch. Brepols et al. / Desalination 231 (2008) 20–2625Fig. 3. Flow diagram of wwtp Bergheim-Glessen.Sludge treatment and simultaneous precipitation are taken over from the today’s continuance. The plant is scheduled to be commissioned in late 2007.4.2. wwtp Rietliau, SwitzerlandUpgrading was necessary to meet the effluent requirements (DOC: 10 mg/l, BOD: 10 mg/l, P total: 0.2 mg/l, SS: 5 mg/l) especially according parameter SS which was unachievable by the former wwtp concept. An upgrading of the treat-ment capacity from 41,400 p.e. up to 44,000 p.e. also would have been accomplished by depth fil-tration as a fourth treatment step. Caused by small space availability the hybrid solution was evalu-ated as an economically more favourable way. Shortage of space is due to the wwtp location in the midst of the residential area Wädenswil, 100m far from the bank of the Lake of Zurich. Fig. 4 shows the flow diagram.Wwtp Rietliau was commissioned in Novem-ber 2005. The treatment process is subdivided into two lines. Each, the MBR line and the conven-tional process line, treat half of the incoming wastewater. Sludge of both treatment lines is not mixed. All wastewater is treated by the existing mechanical pre-treatment units (screen, grit cham-ber and grease trap, primary sedimentation). In addition, the inflow from the primary sedimenta-tion to the MBR line is led through a sieve con-sisting of hole geometry with 1 mm gap size.The MBR line consists of two sub-lines. Aero-bic and anoxic volumes of the MBR process are dimensioned the way, that in times of maximum inflow the minimum HRT within the biological zone prior to the filtration chambers does not fall below 30min.Better effluent quality concerning the conven-tional process line also is achieved caused by the less hydraulic load of the secondary clarifiers. Thus, the requirements that have to be met by the mixture of both effluent streams can be guaran-teed.5. ConclusionsThe presented upgrading concepts raise no claim to completeness and thus reveal the wide spectrum of supposable measures. Many of them are under investigation and appropriate findings can be expected to be reported soon. However, the chosen upgrading concept must meet the claim to be•demand-oriented according the wastewater-sided requirements and the load situation,•economical in view of annual costs (operating expenses and net debt service).Besides, various other, not only process-re-lated, but also nonmonetary and monetary hardly assessable aspects are to be followed and to weigh in each individual case which do not admit a stan-26Ch. Brepols et al. / Desalination 231 (2008) 20–26conventional activated sludge process Fig. 4. Flow diagram of wwtp Rietliau.dard approach concerning the handling of the planning task.Altogether MBR technology provides several promising perspectives in view of upgrading wwtps. The different options introduced provide an overview of the bunch of possibilities the op-timal solution can be selected from. As with all other upgrading options which in general are in-dividual solutions, special importance lies on the adequate diligence of the planning engineer. Nev-ertheless the increasing number of full scale ap-plications presents a sound and ever growing de-cision basis.References[1]J. Krampe and Kh. Krauth, Das Sequencing BatchReactor-Membranbelebungsverfahren. 4. ATSV, Aachen, 2001.[2]W. Schier, An exemplary approach for the integra-tion of new sizing procedures and new purification technologies for the performance of wwtps, Scripts W ATER • W ASTEW ATER • W ASTE of Department of Sanitary and Environmental Engineering —DESEE and Department of Waste Engineering ofthe University of Kassel, issue 22, Kassel Univer-sity Press, 2003.[3] F.-B. Frechen, W. Schier, M. Wett and A. Waldhoff,The non-conventional low MLSS MBR technology, IWA Specialty Conference Water Environment –Membrane Technology (WEMT), Seoul, Korea, 2004.[4] A. Drews, M. V ocks, V. Iversen, B. Lesjean and M.Kraume, Fouling in Membranbelebungsreaktoren: Erfahrungen beim Betrieb mit diskontinuierlichem Schlammabzug, Chemie Ingenieur Technik, 77 (2005) 593–599.[5] A. Pollice, A. Brookes, B. Jefferson and S. Judd,Subcritical flux fouling in membrane bioreactors —a review of recent literature. Desalination, 174(2005) 221–230.[6]M. Wett, Fouling behaviour of a submerged mem-brane bioreactor for domestic waste water and its influence to the process efficiency, Scripts WATER • W ASTEWATER • W ASTE of Department of Sani-tary and Environmental Engineering — DESEE and Department of Waste Engineering of the University of Kassel, issue 26, Kassel University Press, 2005.[7]Water Environment Federation, Upgrading and Ret-rofitting Water and Wastewater Treatment Plants, Manual of Practice No. 28, McGraw-Hill, USA, 2004.。