Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Land-atmosphere interactions the LoCo perspective
    Santanello, Joseph A. ; Dirmeyer, Paul A. ; Ferguson, Craig R. ; Findell, Kirsten L. ; Tawfik, Ahmed B. ; Berg, Alexis ; Ek, Michael ; Gentine, Pierre ; Guillod, Benoit P. ; Heerwaarden, Chiel van; Roundy, Joshua ; Wulfmeyer, Volker - \ 2018
    Bulletin of the American Meteorological Society 99 (2018)6. - ISSN 0003-0007 - p. 1253 - 1272.

    Metrics derived by the LoCo working group have matured and begun to enter the mainstream, signaling the success of the GEWEX approach to foster grassroots participation.

    Burden of diarrhea in the eastern mediterranean region, 1990-2013 : Findings from the global burden of disease study 2013
    Khalil, Ibrahim ; Colombara, Danny V. ; Forouzanfar, Mohammad Hossein ; Troeger, Christopher ; Daoud, Farah ; Moradi-Lakeh, Maziar ; Bcheraoui, Charbel El; Rao, Puja C. ; Afshin, Ashkan ; Charara, Raghid ; Abate, Kalkidan Hassen ; Abd El Razek, Mohammed Magdy ; Abd-Allah, Foad ; Abu-Elyazeed, Remon ; Kiadaliri, Aliasghar Ahmad ; Akanda, Ali Shafqat ; Akseer, Nadia ; Alam, Khurshid ; Alasfoor, Deena ; Ali, Raghib ; AlMazroa, Mohammad A. ; Alomari, Mahmoud A. ; Salem Al-Raddadi, Rajaa Mohammad ; Alsharif, Ubai ; Alsowaidi, Shirina ; Altirkawi, Khalid A. ; Alvis-Guzman, Nelson ; Ammar, Walid ; Antonio, Carl Abelardo T. ; Asayesh, Hamid ; Asghar, Rana Jawad ; Atique, Suleman ; Awasthi, Ashish ; Bacha, Umar ; Badawi, Alaa ; Barac, Aleksandra ; Bedi, Neeraj ; Bekele, Tolesa ; Bensenor, Isabela M. ; Betsu, Balem Demtsu ; Bhutta, Zulfiqar ; Abdulhak, Aref A. Bin; Butt, Zahid A. ; Danawi, Hadi ; Dubey, Manisha ; Endries, Aman Yesuf ; Faghmous, Imad M.D.A. ; Farid, Talha ; Farvid, Maryam S. ; Farzadfar, Farshad ; Fereshtehnejad, Seyed Mohammad ; Fischer, Florian ; Anderson Fitchett, Joseph Robert ; Gibney, Katherine B. ; Mohamed Ginawi, Ibrahim Abdelmageem ; Gishu, Melkamu Dedefo ; Gugnani, Harish Chander ; Gupta, Rahul ; Hailu, Gessessew Bugssa ; Hamadeh, Randah Ribhi ; Hamidi, Samer ; Harb, Hilda L. ; Hedayati, Mohammad T. ; Hsairi, Mohamed ; Husseini, Abdullatif ; Jahanmehr, Nader ; Javanbakht, Mehdi ; Beyene, Tariku ; Jonas, Jost B. ; Kasaeian, Amir ; Khader, Yousef Saleh ; Khan, Abdur Rahman ; Khan, Ejaz Ahmad ; Khan, Gulfaraz ; Khoja, Tawfik Ahmed Muthafer ; Kinfu, Yohannes ; Kissoon, Niranjan ; Koyanagi, Ai ; Lal, Aparna ; Abdul Latif, Asma Abdul ; Lunevicius, Raimundas ; Abd El Razek, Hassan Magdy ; Majeed, Azeem ; Malekzadeh, Reza ; Mehari, Alem ; Mekonnen, Alemayehu B. ; Melaku, Yohannes Adama ; Memish, Ziad A. ; Mendoza, Walter ; Misganaw, Awoke ; Ibrahim Mohamed, Layla Abdalla ; Nachega, Jean B. ; Nguyen, Quyen Le ; Nisar, Muhammad Imran ; Peprah, Emmanuel Kwame ; Platts-Mills, James A. ; Pourmalek, Farshad ; Qorbani, Mostafa ; Rafay, Anwar ; Rahimi-Movaghar, Vafa ; Ur Rahman, Sajjad ; Rai, Rajesh Kumar ; Rana, Saleem M. ; Ranabhat, Chhabi L. ; Rao, Sowmya R. ; Refaat, Amany H. ; Riddle, Mark ; Roshandel, Gholamreza ; Ruhago, George Mugambage ; Saleh, Muhammad Muhammad ; Sanabria, Juan R. ; Sawhney, Monika ; Sepanlou, Sadaf G. ; Setegn, Tesfaye ; Sliwa, Karen ; Sreeramareddy, Chandrashekhar T. ; Sykes, Bryan L. ; Tavakkoli, Mohammad ; Tedla, Bemnet Amare ; Terkawi, Abdullah S. ; Ukwaja, Kingsley ; Uthman, Olalekan A. ; Westerman, Ronny ; Wubshet, Mamo ; Yenesew, Muluken A. ; Yonemoto, Naohiro ; Younis, Mustafa Z. ; Zaidi, Zoubida ; Sayed Zaki, Maysaa El; Rabeeah, Abdullah A. Al; Wang, Haidong ; Naghavi, Mohsen ; Vos, Theo ; Lopez, Alan D. ; Murray, Christopher J.L. ; Mokdad, Ali H. - \ 2016
    American Journal of Tropical Medicine and Hygiene 95 (2016)6. - ISSN 0002-9637 - p. 1319 - 1329.

    Diarrheal diseases (DD) are leading causes of disease burden, death, and disability, especially in children in low-income settings. DD can also impact a child's potential livelihood through stunted physical growth, cognitive impairment, and other sequelae. As part of the Global Burden of Disease Study, we estimated DD burden, and the burden attributable to specific risk factors and particular etiologies, in the Eastern Mediterranean Region (EMR) between 1990 and 2013. For both sexes and all ages, we calculated disability-adjusted life years (DALYs), which are the sum of years of life lost and years lived with disability. We estimate that over 125,000 deaths (3.6% of total deaths) were due to DD in the EMR in 2013, with a greater burden of DD in low-and middle-income countries. Diarrhea deaths per 100,000 children under 5 years of age ranged from one (95% uncertainty interval [UI] = 0-1) in Bahrain and Oman to 471 (95% UI = 245-763) in Somalia. The pattern for diarrhea DALYs among those under 5 years of age closely followed that for diarrheal deaths. DALYs per 100,000 ranged from 739 (95% UI = 520-989) in Syria to 40,869 (95% UI = 21,540-65,823) in Somalia. Our results highlighted a highly inequitable burden of DD in EMR, mainly driven by the lack of access to proper resources such as water and sanitation. Our findings will guide preventive and treatment interventions which are based on evidence and which follow the ultimate goal of reducing the DD burden.

    Negative Epistasis and Evolvability in TEM-1 ß-Lactamase- The Thin Line between an Enzyme's Conformational Freedom and Disorder
    Dellus-Gur, E. ; Elias, M. ; Caselli, E. ; Prati, F. ; Salverda, M.L.M. ; Visser, J.A.G.M. de; Fraser, J.S. ; Tawfik, D.S. - \ 2015
    Journal of Molecular Biology 427 (2015)14. - ISSN 0022-2836 - p. 2396 - 2409.
    empirical fitness landscapes - antibiotic-resistance - protein structures - escherichia-coli - substrate-specificity - sequence space - sign epistasis - omega-loop - trade-offs - evolution
    Epistasis is a key factor in evolution since it determines which combinations of mutations provide adaptive solutions and which mutational pathways toward these solutions are accessible by natural selection. There is growing evidence for the pervasiveness of sign epistasis—a complete reversion of mutational effects, particularly in protein evolution—yet its molecular basis remains poorly understood. We describe the structural basis of sign epistasis between G238S and R164S, two adaptive mutations in TEM-1 ß-lactamase— an enzyme that endows antibiotics resistance. Separated by 10 Å, these mutations initiate two separate trajectories toward increased hydrolysis rates and resistance toward second and third-generation cephalosporins antibiotics. Both mutations allow the enzyme's active site to adopt alternative conformations and accommodate the new antibiotics. By solving the corresponding set of crystal structures, we found that R164S causes local disorder whereas G238S induces discrete conformations. When combined, the mutations in 238 and 164 induce local disorder whereby nonproductive conformations that perturb the enzyme's catalytic preorganization dominate. Specifically, Asn170 that coordinates the deacylating water molecule is misaligned, in both the free form and the inhibitor-bound double mutant. This local disorder is not restored by stabilizing global suppressor mutations and thus leads to an evolutionary cul-de-sac. Conformational dynamism therefore underlines the reshaping potential of protein's structures and functions but also limits protein evolvability because of the fragility of the interactions networks that maintain protein structures
    Initial mutations direct alternative pathways of protein evolution
    Salverda, M.L.M. ; Dellus, E. ; Gorter, F.A. ; Debets, A.J.M. ; Oost, J. van der; Hoekstra, R.F. ; Tawfik, D.S. ; Visser, J.A.G.M. de - \ 2011
    Plos Genetics 7 (2011)3. - ISSN 1553-7404 - 11 p.
    tem-1 beta-lactamase - empirical fitness landscapes - in-vitro - natural evolution - escherichia-coli - antibiotic-resistance - sequence space - adaptation - epistasis - trajectories
    Whether evolution is erratic due to random historical details, or is repeatedly directed along similar paths by certain constraints, remains unclear. Epistasis (i.e. non-additive interaction between mutations that affect fitness) is a mechanism that can contribute to both scenarios. Epistasis can constrain the type and order of selected mutations, but it can also make adaptive trajectories contingent upon the first random substitution. This effect is particularly strong under sign epistasis, when the sign of the fitness effects of a mutation depends on its genetic background. In the current study, we examine how epistatic interactions between mutations determine alternative evolutionary pathways, using in vitro evolution of the antibiotic resistance enzyme TEM-1 ß-lactamase. First, we describe the diversity of adaptive pathways among replicate lines during evolution for resistance to a novel antibiotic (cefotaxime). Consistent with the prediction of epistatic constraints, most lines increased resistance by acquiring three mutations in a fixed order. However, a few lines deviated from this pattern. Next, to test whether negative interactions between alternative initial substitutions drive this divergence, alleles containing initial substitutions from the deviating lines were evolved under identical conditions. Indeed, these alternative initial substitutions consistently led to lower adaptive peaks, involving more and other substitutions than those observed in the common pathway. We found that a combination of decreased enzymatic activity and lower folding cooperativity underlies negative sign epistasis in the clash between key mutations in the common and deviating lines (Gly238Ser and Arg164Ser, respectively). Our results demonstrate that epistasis contributes to contingency in protein evolution by amplifying the selective consequences of random mutations
    Polyurethane rotating disc system for post-treatment of anaerobically pre-treated sewage
    Tawfik, A. ; Klapwijk, A. - \ 2010
    Journal of Environmental Management 91 (2010)5. - ISSN 0301-4797 - p. 1183 - 1192.
    municipal waste-water - biological contactor rbc - domestic sewage - nitrogen removal - escherichia-coli - bacteria - effluent - biofilm - feasibility - performance
    The performance of polyurethane rotating discs (RBC-1) versus polystyrene rotating discs (RBC-2) for the treatment of an up-flow anaerobic sludge blanket (UASB) reactor effluent fed with domestic wastewater was investigated. Both RBC units were operated at the same organic loading rate (OLR) of 10.5 gCOD/m(2) d. and a hydraulic retention time (HRT) of 2.5 h. The residual values of COD fractions (CODsuspended, CODcolloidal and CODsoluble) in the treated effluent of RBC-1 and RBC-2 were similar. However, the removal efficiency of ammonia in the RBC-1 (87 +/- 4%) was significantly higher than that found for RBC-2 i.e. 24 +/- 6%. Moreover, RBC-1 achieved a substantial removal efficiency of 99.0 +/- 1% for Escherichia colt (E. coli), while RBC-2 removed 91.2 +/- 0.3%. Based on these results, optimization of RBC-1 treating UASB reactor effluent was extensively performed. The RBC-1 was operated at an OLR's of 4.0, 11 and 23 gCOD/m(2) d. The results obtained showed that increasing the OLR from 11.0 to 23.0 gCOD/m(2) d and decreasing the HRT from 2.5 to 1.25 h significantly declined the effluent quality of CODtotal and ammonia. However, the residual values of CODtotal and ammonia remained unaffected when increasing the OLR from 4.0 to 11.0 gCOD/m(2) d and by decreasing the HRT from 5 to 2.5 h. Bacteriological examination showed that the mean residual count of E. coli remained at a level of 10(4)/100 ml, in the effluent of RBC-1 independent on the imposed HRT. Accordingly, it is recommended to operate RBC-1 for treatment of anaerobically pre-treated sewage at an OLR of 11 gCOD/m(2) d and an HRT of 2.5 h. A feed-less (ammonia limitation) period of 9.0 days followed by 9.0 days feeding with high OLR of 26 gCOD/m(2) d. (raw sewage) was investigated to elaborate, if the nitrifiers of the RBC-1 are capable to convert ammonia to nitrate after totally 18 days when retuning back to the normal operating conditions. The results of the experiment clearly show a strong and immediate detrimental effect of imposing high OLR of 26 gCOD/m(2) d on the nitrification process in the nitrifying RBC unit. However, after returning back to the original OLR of 10.6 gCOD/m(2) d, the nitrification efficiency in the RBC unit was recovered within 2-3 days.
    Treatment of domestic wastewater in an up-flow anaerobic sludge blanket reactor followed by moving bed biofilm reactor
    Tawfik, A. ; El-Gohary, F. ; Temmink, B.G. - \ 2010
    Bioprocess and Biosystems Engineering 33 (2010)2. - ISSN 1615-7591 - p. 267 - 276.
    sponge dhs system - nitrogen removal - low-temperatures - uasb reactors - sewage - denitrification - nitrification - retention - effluent - time
    The performance of a laboratory-scale sewage treatment system composed of an up-flow anaerobic sludge blanket (UASB) reactor and a moving bed biofilm reactor (MBBR) at a temperature of (22-35 A degrees C) was evaluated. The entire treatment system was operated at different hydraulic retention times (HRT's) of 13.3, 10 and 5.0 h. An overall reduction of 80-86% for CODtotal; 51-73% for CODcolloidal and 20-55% for CODsoluble was found at a total HRT of 5-10 h, respectively. By prolonging the HRT to 13.3 h, the removal efficiencies of CODtotal, CODcolloidal and CODsoluble increased up to 92, 89 and 80%, respectively. However, the removal efficiency of CODsuspended in the combined system remained unaffected when increasing the total HRT from 5 to 10 h and from 10 to 13.3 h. This indicates that, the removal of CODsuspended was independent on the imposed HRT. Ammonia-nitrogen removal in MBBR treating UASB reactor effluent was significantly influenced by organic loading rate (OLR). 62% of ammonia was eliminated at OLR of 4.6 g COD m(-2) day(-1). The removal efficiency was decreased by a value of 34 and 43% at a higher OLR's of 7.4 and 17.8 g COD m(-2) day(-1), respectively. The mean overall residual counts of faecal coliform in the final effluent were 8.9 x 10(4) MPN per 100 ml at a HRT of 13.3 h, 4.9 x 10(5) MPN per 100 ml at a HRT of 10 h and 9.4 x 10(5) MPN per 100 ml at a HRT of 5.0 h, corresponding to overall log(10) reduction of 2.3, 1.4 and 0.7, respectively. The discharged sludge from UASB-MBBR exerts an excellent settling property. Moreover, the mean value of the net sludge yield was only 6% in UASB reactor and 7% in the MBBR of the total influent COD at a total HRT of 13.3 h. Accordingly, the use of the combined UASB-MBBR system for sewage treatment is recommended at a total HRT of 13.3 h.
    Sewage treatment in a rotating biological contactor (RBC) system
    Tawfik, A. ; Temmink, B.G. ; Zeeman, G. ; Klapwijk, A. - \ 2006
    Water Air and Soil Pollution 175 (2006)1-4. - ISSN 0049-6979 - p. 275 - 289.
    suspended-growth reactor - domestic sewage - supplemental aeration - escherichia-coli - nitrification - performance - oxygen - wastewaters - removal
    The treatment of domestic wastewater at a temperature of 12¿24°C was investigated in an RBC system. The RBC consists of a two stage system connected in series. The system was operated at different organic loading rates (OLR's) and hydraulic retntion times (HRT's) in order to optimize the RBC performance. The overall removal efficiencies for chemical oxygen demand (CODtotal, CODsuspended and CODcolloidal) significantly decreased when decreasing the total HRT from 10 to 2.5 h and increasing the OLR from 11 to 47 g COD/m2.d. However, the effluent quality of CODsoluble remained unaffected. Most of the COD was removed in the 1st stage and nitrification took place in the 2nd stage of the two stage system.The overall nitrification efficiency was 49% at total OLR of 11 gCOD/m2.d. At total HRT's of 10, 5 and 2.5 h, the Escherchia coli (E. coli) concentration was reduced by a value of 1.6, 1.5 and 0.8 log10 respectively. The sludge volume index (SVI) decreased as the OLR increased. However, the SVI of the excess sludge produced in the RBC under different OLR's was always
    Potentials of using a rotating biological contactor (RBC) for post-treatment of anaerobically pre-treated domestic wastewater
    Tawfik, A. ; Klapwijk, A. ; El-Gohary, F. ; Lettinga, G. - \ 2005
    Biochemical Engineering Journal 25 (2005)1. - ISSN 1369-703X - p. 89 - 98.
    nitrogen removal - sewage-treatment - denitrification - feasibility - wastewaters - system
    This study has been carried out in order to assess the impact of CODhiod in an UASB effluent applied to a single stage, a two stage RBC system and an anoxic up-flow submerged bio-filter followed by a segmental two stage aerobic RBC on the removal efficiency of different COD fractions, Escherichia coli, ammonia and partially nitrate removal. The two (single stage) RBC's were operated at a constant HRT of 2.5 h and temperature of 21 degrees C but at different OLR's, viz. of 10 and 14 g CODbiod/m(2) day due to the highly different UASB effluent qualities. The results clearly show that the residual values of CODtotal, ammonia and E. coli in the final effluent are significantly lower at the lower imposed OLR of 10 g COD (hiod)/m(2) day. In view of the results obtained we recommend to use a single stage RBC system at OLR of 10 g CODhiod/m(2) day and at HRT of 2.5 h for post-treatment of the effluent of UASB reactor operated at high temperature of 30 degrees C as generally prevails in tropical countries. The performance of a single stage versus two stage RBC system for post-treatment of the effluent of an UASB reactor operated at a low temperature of 12 degrees C has been evaluated. The single stage and a two stage RBC system were operated at the same OLR of 18 g CODbiod/m(2) day and at HRT of 2.5 h. The results show that the COD fractions, ammonia and E. coli content in the final effluent of a two stage RBC system were significantly lower than the effluent of the single stage RBC system. Accordingly, we recommend a two stage RBC system at an HRT of 2.5 h and OLR of 18 g CODbiod/m(2) day for post-treatment of the effluent of a conventional UASB reactor operating at a low temperature of 12 degrees C. The nitrogen removal from the nitrified effluent was investigated using a biofilm system consisting of three stages, viz. an anoxic up-flow submerged bio-filter followed by a segmental two stage aerobic RBC. The nitrified effluent of the second stage RBC was recycled to the anoxic up-flow submerged bio-filter reactor. The results obtained reveal that the introduction of an anoxic reactor as a first stage combined with recirculation of the nitrified effluent of the second stage RBC is accompanied with a conversion of nitrate into ammonia, at least in case the content of CODbiod. in the UASB effluent is low. In such a situation the ammonia needs to be nitrified two times, which obviously should be avoided. Therefore in such situations of a too high quality anaerobic effluent in terms of biodegradable COD content, the introduction of a separate anoxic reactor for denitrification as final post-treatment step can not be recommended. (c) 2005 Elsevier B.V. All rights reserved.
    Treatment of domestic sewage in a combined UASB/RBC system. Process optimization for irrigation purposes
    Tawfik Ibrahim, A. ; Zeeman, G. ; Klapwijk, A. ; Sanders, W.T.M. ; El-Gohary, F. ; Lettinga, G. - \ 2003
    Water Science and Technology 48 (2003)1. - ISSN 0273-1223 - p. 131 - 138.
    waste-water - wastewaters - contactor
    A Rotating Biological Contactor (RBC) was fed with raw domestic wastewater or anaerobic effluents. The experiments were conducted at increasing operational temperatures viz. 11, 20 and 30degreesC to assess the potential increase in removal efficiencies for the different COD fractions (CODtotal, CODsuspended, CODcolloidal and CODsoluble), E. coli and in the nitrification rate. The results clearly show that, the RBC at HRT of 2.5 h and OLR of 47 gCOD/m(2).d provided a very high residual CODtotal value of 228 mg/l when treating domestic wastewater. This was not the case as compared to the results obtained for the system when operated at the same HRT but at lower OLR's of 27, 20 and 14.5 g COD/m(2).d with a UASB effluent at operational temperatures of 11, 20 and 30degreesC respectively. The residual CODtotal values amounted to 100, 85 and 72 mg/l in the final effluents. Moreover, a high removal of ammonia and low residual values of E. coli was found for the RBC when treating a UASB effluent at operational temperature of 30degreesC as compared to the situation for treatment of domestic wastewater and UASB effluent at lower temperatures of 11 and 20degreesC. It can be concluded that an efficient pre-treatment of sewage implies a substantial reduction of OLR applied to the RBC and consequently improves the residual of CODtotal, ammonia and E. coli in the final effluent. Therefore, this study supports using a combined system UASB/RBC for treatment of domestic wastewater for reuse in irrigation.
    Anaerobic digestion and physiological waste and kitchen refuse towards resource management in the DESAR concept
    Kujawa, K. ; Elmitwally, T.A. ; Leeuwen, M. van; Tawfik Ibrahim, A. ; Mes, T.Z.D. de; Zeeman, G. - \ 2003
    In: Proceedings of the 2nd IWA/GTZ international symposium on ecological sanitation. - Lubeck, Germany : - p. 499 - 507.
    Treatment of domestic sewage in a Combined UASB/RBC system : process optimization for irrigation purposes
    Tawfik, A. ; Zeeman, G. ; Klapwijk, A. ; Sanders, W.T.M. ; Gohary, F. El; Lettinga, G. - \ 2002
    In: Proceedings of the International Conference From nutrient removal to recovery, Amsterdam, The Netherlands, 2002 - p. 8 - 8.
    Treatment of Domestic Sewage in Mediterranean Countries Using a UASB Reactor Followed by Polyurethane Rotating Discs
    Tawfik, A. ; Zeeman, G. ; Klapwijk, A. ; Sanders, W.T.M. ; El-Gohary, F. ; Lier, J.B. van; Lettinga, G. - \ 2002
    In: Proceedings Regional Symposium on Water Recycling in Mediterranean Region, Iraklio, Greece - p. 275 - 282.
    Treatment of anaerobically treated domestic wastewater using rotating biological contactor
    Tawfik, A. ; Klapwijk, A. ; El-Gohary, F. ; Lettinga, G. - \ 2002
    Water Science and Technology 45 (2002)10. - ISSN 0273-1223 - p. 371 - 176.
    afvalwaterbehandeling - fecale coliformen - rioolafvalwater - ronddraaiende biologische contactbedden - biologische behandeling - waste water treatment - faecal coliforms - sewage effluent - rotating biological contactors - biological treatment
    A small-scale pilot plant consisting of a three-stage RBC has been investigated for the removal of E. coli, COD fractions and ammonia from the effluent of an UASB reactor treating domestic wastewater. The results obtained reveal that a three-stage system operated at a HRT of 3.0 h represents an effective posttreatment process. The remaining COD in the final effluent was only 51 ( /- 7) mgl(-1). Ammonia concentration was reduced by 67 ( /- 7.6) ÐThe overall E. coli reduction was 1.39 log10 at an influent count of 6.5 log10 corresponding to an overall removal efficiency of 95.8 ( /- 4.7) ÐHowever, according to prevailing standards, residual E. coli counts are still high for unrestricted reuse for irrigation purposes. When the system was operated at a HRT of 10 h, overall E. coli removal and ammonia reduction were 99.9 ( /- 0.05)nd 92 ( /- 6.5) ␛espectively. At a HRT of 10 h, recirculation of the 3rd stage effluent to the 1st stage reduced the residual of E. coli in the final effluent from 2 x 10(3) to 9.8 x 10(2)/100ml. Moreover, the recirculation of nitrified effluent from the 3rd stage to the 1st stage increased ammonia removal in the stage 1 from 23 to 43ÐThis relatively high ammonia removal likely can be attributed to the supply of nitrifiers from 3rd stage to the 1st one.
    The biorotor system for post-treatment of anaerobically treated domestic sewage
    Tawfik, A. - \ 2002
    Wageningen University. Promotor(en): G. Lettinga; F. El-Gohary; A. Klapwijk. - S.l. : S.n. - ISBN 9789058085658 - 140
    anaërobe behandeling - rioolafvalwater - sedimentatie - escherichia coli - anaerobic treatment - sewage effluent - sedimentation - escherichia coli

    This thesis describes the evaluation of the applicability of biorotor system for post-treatment (polishing) of different effluent qualities of an UASB reactor treating raw domestic sewage, with emphasis on the elimination of various COD fractions, ammonia and E.Coli.

    The removal mechanism of E.Coli from UASB effluent using a RBC has been investigated. The results obtained revealed that an adsorption process and sedimentation comprise the most important removal mechanism of E.Coli in the biofilm. Die-off is relatively minor importance as removal mechanism in a RBC system.

    The performance of an anaerobic versus aerobic RBC system treating a high quality UASB reactor effluent was investigated at the same HRT and OLR. The results obtained indicated that the removal efficiency of the COD fractions and of E.Coli fractions found in the aerobic RBC significantly exceeds that of the anaerobic unit. Therefore, the results of our investigations strongly support the use of an aerobic RBC as a post-treatment step of UASB reactor effluents.

    When applying a single and two stage aerobic RBC at the same OLR of 14.5 g COD total .m -2.d -1and at a HRT of 2.5 h., but at different temperatures of 24 and 17 °C respectively, both systems provided the same residual effluent values for COD total (72 mg l -1), for COD suspended (16 mg l -1), for COD colloidal (5 mg l -1) and for COD soluble (51 mg l -1). Moreover, also the removal efficiency of E.Coli was almost the same, viz. amounting to 94 %. However, the ammonia removal in the single stage RBC amounted to 50 % of which 71 % was nitrified, compared to only 23 % in the two-stage system. This better performance can be attributed to the higher temperature of the wastewater during the operation of the single stage RBC system. In view of these results, we recommend to use a single stage RBC system for COD removal and for a partial nitrification and E.Coli removal at OLR of 14.5 g COD total .m -2.d -1and at HRT of 2.5 h for post-treatment of a high quality UASB reactor effluent.

    We investigated the use of anoxic reactor followed by a segmental two stage aerobic RBC for nitrogen removal from the nitrified effluent. The results obtained reveal that the introduction of an anoxic reactor as a 1 ststage combined with recirculation of the nitrified effluent of the 2 ndstage RBC is accompanied with a conversion of nitrate into ammonia, at least in case the content of COD biod. in the UASB effluent is low. Therefore, the introduction of a separate anoxic reactor for denitrification as final post-treatment step can not be recommended in such a situation.

    In one of the experiments the UASB reactor was operated at two different operational temperatures viz. of 30 and 11°C resulting in quite different COD biod. concentrations in the UASB effluent. For the post-treatment of this highly different effluent a single stage RBC was operated at a constant HRT of 1.25 h., consequently at COD biod. loading rates of 17.7 and 36.8 g m -2. d -1. The results clearly show that the residual values of COD fractions and E.Coli are significantly lower at the lower imposed COD biod. loading rate of 17.7g COD biod. m -2. d -1. We also compared the efficiency of the two-stage RBC system for this highly different UASB effluent, viz. once again at the same HRT (2.5 h) and at COD biod. loading rate of 9 and 18 g m -2. d -1. The results reveal that with the two-stage RBC system the residual values of distinguished COD fractions in the final effluent were almost the same, but the residual value of E.Coli in the final effluent amounted to 3.4 x 10 5at the higher COD biod. loading rate and to 7.6 x 10 4/100 ml at the lower one. Moreover, the calculated nitrification rate in the 2 ndstage of two stage RBC system dropped from 1.56 to 1.1 g NO 3 -N.m -2.d -1with an increase the COD biod. loading rate from 11.3 to 16 g m -2.d -1. The results clearly demonstrate that the introduction of a well performing UASB reactor not only improves the nitrification rate but also the E.Coli removal in the post-treatment system.

    We compared the performance of the single with that of a two-stage RBC for the treatment of poor quality UASB reactor effluent. The results obtained showed that the COD fractions and the E.Coli content in the final effluent of a two stage were lower than in the effluent of the single stage RBC. Moreover, The calculated nitrification rate in the single stage was much lower compared with the two stages RBC. Based on these results we recommend a two stage RBC system for post-treatment of poor quality UASB reactor effluent. The two-stage system was operated at different HRT's and OLR's in order to assess better design criteria for the system. The removal efficiencies for the various COD fractions decreased only slightly when decreasing the HRT from 10 to 2.5 h., and increasing the OLR from 6.45 to 24 g COD total m -2.d -1. However, the overall nitrification efficiency and E.Coli were negatively affected when increasing the loading conditions in the range investigated. The results found for E.Coli removal revealed that the major part of suspended E.Coli (>4.4 µm) was eliminated by sedimentation or by adsorption in the biofilm of the 1 ststage (99.66 %). However, E.Coli present in the colloidal fraction (< 4.4 - > 0.45 µm) was eliminated in the 2 ndstage of two stage RBC (99.78 %). Based on these results we recommend for the treatment of a poor UASB effluent quality the use of two stages RBC system for the removal of COD fractions and ammonia and for a partial removal of E.Coli at HRT of 10 h and OLR of 6.45 g COD total .m -2.d -1.

    The effluent of two stages still cannot be used for unrestricted irrigation purposes, at least according to the standards provided by the WHO with respect to the E.Coli content. Therefore, in order to meet these (very stringent) standards, we investigated the use of a three stage RBC-system for post-treatment of an effluent from a rather poorly performing UASB reactor. This three stage RBC was first operated at a HRT of 3.0 h. Under these conditions the E.Coli count in the final effluent was still too high. However, when applying an HRT of 10 h., the E.Coli content complied almost the WHO standards for unrestricted irrigation purposes. Therefore, when such high removal efficiency for E.Coli really would be required, the best solution is to use three independent stages at HRT of 10 h., which then obviously implies very significantly investment and operational costs.

    Treatment of anaerobically pre-treated domestic sewage by a rotating biological contactor
    Tawfik, A. ; Klapwijk, A. ; el-Gohary, F. ; Lettinga, G. - \ 2002
    Water Research 36 (2002)1. - ISSN 0043-1354 - p. 147 - 155.
    afvalwaterbehandeling - nitrificatie - rioolafvalwater - anaërobe behandeling - zuurstof - retentie - escherichia coli - chemisch zuurstofverbruik - biologische behandeling - waste water treatment - nitrification - sewage effluent - anaerobic treatment - oxygen - retention - escherichia coli - chemical oxygen demand - biological treatment
    The performance of a rotating biological contactor (RBC) for the post-treatment of the effluent of an up-flow anaerobic sludge blanket (UASB) was the subject of this study. Different hydraulic and organic loading rates have been investigated. The removal efficiencies of CODtotal, CODsuspended, CODcolloidal and CODsoluble increased at a higher hydraulic retention time (HRT) and a lower influent organic loading rate.The results obtained indicated that a two-stage RBC reactor at an HRT of 10h and an organic loading rate of 6.4g CODm-2d-1 represents an effective post-treatment process. Most CODsuspended and CODcolloidal were removed in the first stage while nitrification proceeded in the second stage.The overall nitrification efficiency was 92% at an ammonia loading rate of 1.1gm-2d-1. Total E. coli removal at HRTs of 10, 5 and 2.5h were 99.5%, 99.0% and 89.0%, respectively. The major part of suspended E. coli (>4.4μm) was removed by sedimentation or by adsorption in the biofilm of the first stage of RBC (99.66%). However, E. coli in the colloidal fraction (<4.4 to >0.45μm) was eliminated in the second stage of RBC (99.78%).A comparison of the performance of a one-stage versus two-stage RBC system, operated at the same total loading rate, revealed an improvement in the effluent quality of the two-stage effluent as compared to the one-stage effluent.The two stages RBC were used to examine the effect of hydraulic shock loads on reactor performance in terms of COD, nitrification and E. coli removal. Copyright
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