Energy Reduction in a Woven-Fabric Immersed Membrane Bioreactor

Deelie, Malcolm (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: Most developing countries, including South Africa, currently face a substantial challenge in providing satisfactory sanitation for all its inhabitants. Small-scale sanitation plants have the greatest potential to overcome this challenge, especially for decentralized areas. Currently such systems are available; however these systems are extremely expensive and complicated, especially in terms of the running costs. In recent years there has been a major shift towards immersed membrane bioreactor (IMBR) technology in the wastewater treatment industry due to the advantages that IMBRs offer over conventional wastewater treatment plants. The major hindrance to the implementation of IMBRs in developing economies is due the costliness and the lack of durability of the current membranes being used. A novel woven-fabric microfilter (WFMF) is currently produced in South Africa from woven polyester which resembles the features of a microfilter and harbours the characteristics to make IMBRs sustainable and affordable. An IMBR which makes use of the WFMF is known as the woven-fabric immersed membrane bioreactor (WF IMBR). The overall aim of this study is to reduce the energy consumption in the WF-IMBR to make it an affordable technology. The following are the key objectives of this study: I. Improve the mechanical design of the WFMF membrane module; II. Improve the air-scour regime of the WF-IMBR; To start the investigation, a pilot plant rig was constructed and set-up at Zandvliet wastewater treatment works (WWTW). Preliminary experiments were done to evaluate the WFMF module design and modify it in order to decrease the inherent pressure drop which would reduce the energy consumed to withdraw permeate from the system. By inserting a more rigid spacer and by including two larger permeate outlets the overall pressure drop was decreased by 90%. Experiments were then performed to investigate the effect of different process conditions. A surprising result, which suggested that less fouling occurred when operating the system without scouring the membrane; led to further investigation of this phenomenon on a lab-scale basis. Lab-scale results confirmed this phenomenon and also gave rise to a new operating regime, known as intermittent air-scouring. Across all three activated sludge feeds from different WWTWs investigated, there was a clear indication that operating with intermittent air-scouring and with air scouring resulted in the lowest fouling rate. This was significantly less than operating with continuous air-scouring. Furthermore, increasing the air-scour rate during continuous air-scouring trials resulted in higher fouling rates. A three factor two level factorial experiment was then performed to investigate the effect of the three main parameters which could potentially increase the effectiveness of the intermittent air-scouring regime. Results showed that filtration duration was one of the more important operational parameters during intermittent air-scour trials. It was hypothesised that longer filtration durations allowed for a protective cake layer to form on the membrane surface which kept the membrane clear of organic substances which has a higher fouling potential. Implementing these findings on the pilot plant rig, confirmed intermittent air-scouring to be the most practical and feasible air-scour regime which reduced air-scour costs by 95%. Further investigations should be done to determine an optimum operating point for intermittent air-scour regime on the pilot plant rig.

AFRIKAANS OPSOMMING: Alle ontwikkelende lande, insluitend Suid-Afrika, het tans 'n aansienlike uitdaging in die verskaffing van bevredigende sanitasie vir alle inwoners. Kleinskaalse sanitasie plante het die grootste potensiaal om hierdie uitdaging te oorkom, veral vir gedesentraliseerde gebiede. Sulke stelsels is tans beskikbaar maar,is baie duur en ingewikkeld , en die bedryfskostes is hoog. ʼn Groot verskuiwings na IMBR tegnologie in die behandeling van afvalwater het die afgelope jare plaas gevind as gevolg van die voordele wat IMBRs bied teenoor die konvensionele afvalwater tegnologie. Die groot hindernis vir die implementering van IMBRs in ontwikkelinde ekonomieë is tewyte aan die beskostigbaarheid en die gebrek aan duursaamheid van die huidige membrane wat gebruik word.ʼn Oorspronklik geweefstof microfilter(WFMF ) is tans geproduseer in Suid – Afrika uit geweefde poliëster wat dieselfde voorkom as ʼn mikrofilter en ook dieselfde eienskappe as ʼn IMBR bevat om dit volhoubare en bekostigbaar te maak.ʼn IMBRs wat gebruik maak vandie WFMF staan bekend as die ʺwoven-fabric immersed membrane bioreactiorʺ (WF-MBR). Die oorhoofse doel van hierdie studie is om die energie verbruik in die WF-IMBR te verminder om dit 'n bekostigbare tegnologie te maak. Die volgende is die belangrikste doelwitte van hierdie studie: I. Verbeter die meganiese ontwerp van die WFMF membraan. II. Verbeter die lug-skure prosedure van die WF-IMBR. Om die ondersoek mee te begin, was 'n loodsaanleg gebou en op Zandvliet WWTW opgerig. Voorlopige eksperimente is gedoen om die WFMF membraanontwerp te evalueer en te verander om sodoende die huidige druk te verminder, wat die energie verbruik van die stelsel ook sal verminder. Deur van 'n meer solide opening gebruik te maak en ook deur die insluiting van twee groter afsetpunte het die algehele druk met 90% afgeneem. Meer eksperimente was uitgevoer om die effek van verskillende prosese te ondersoek. 'n Verrassende resultaat, het getoon dat, wanneer die stelsel sonder lug gebruik word, dit tot minder aangroei lei. Hierdie resultaat het tot verdere ondersoek van hierdie verskynsel op 'n laboratorium skaal basis aanleiding gegee. Laboratorium-skaal resultate het hierdie verskynsel bevestig en ook aanleiding tot nuwe bedryfstelsel prosedure gegee, wat bekend staan as intermitterende lug-skuur. Al drie geaktiveerde slyk monsters van verskillende afvalwater plante wat ondersoek was,was daar 'n duidelike aanduiding dat die prosedure met intermitterende lug-skuur tot gevolg gehad dat die minste hoeveelheid besoedeling aansienlik minder is as die prosedure met deurlopende lug-skuur. Verder, die verhoging van die lug-skure koers tydens die deurlopende lug-skuur proewe het tot hoër aangroei hoeveelheid gelei. ʼn Drie- faktoor twee- vlak- faktoor eksperiment was toe uitgevoer om die effek van die drie belangrikste veranderings ondersoek wat potensieel die doeltreffendheid van die onderbroke lug-skuur prosedure kan verhoog. Resultate het getoon dat die belangrikste faktor die tydsduur van die filtrasie was. Dit het daarop neer gekom, die feit dat meer filtrasie tyd toegelaat word om 'n beskermende slyk laag te vorm op die membraan oppervlak wat die membraan skoon hou van stowwe soos EPS wat 'n hoër aangroei potensiaal het. Implementering van hierdie bevindinge op die loodsaanleg bevestig dat intermitterende lug-skuur die mees praktiese en haalbare lug-skuur prosedure is wat lug-skure koste met 95% verminder het. Verdere ondersoeke moet gedoen word om 'n optimale bedryfstelsel vir intermitterende lug-skuur prosedure op die loodsaanleg te bepaal.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101011
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