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.

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    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.
    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.
    Nutrients valorisation via duckweed-based wastewater treatment and aquaculture
    El-Shafai, S.A.A.M. - \ 2004
    Wageningen University. Promotor(en): H.J. Gijzen; F. El-Gohary, co-promotor(en): Johan Verreth; P. van der Steen. - [S.l.] : Balkema - ISBN 9789058089564 - 174
    afvalwaterbehandeling - aquacultuur - lemna - voedingsstoffen - egypte - waste water treatment - aquaculture - lemna - nutrients - egypt
    Apparent digestibility coefficient of duckweed (Lemna minor), fresh and dry for Nile tilapia (Oreochromis niloticus L.)
    El-Shafai, S.A.A.M. ; El-Gohary, F. ; Verreth, J.A.J. ; Schrama, J.W. ; Gijzen, H.J. - \ 2004
    Aquaculture Research 35 (2004)6. - ISSN 1355-557X - p. 574 - 586.
    trout oncorhynchus-mykiss - bass dicentrarchus-labrax - dietary-protein sources - acid-insoluble ash - rainbow-trout - nutrient digestibility - feed ingredients - morone-saxatilis - body-composition - striped bass
    Dry matter (DMD), protein (PD), ash (AD), fat (FD), gross energy (ED) and phosphorus (PhD) digestibility coefficients were determined for five different iso-N fish diets fed to Nile tilapia (Oreochromis niloticus). The control diet contained fishmeal (35%), corn (29%), wheat (20%), wheat bran (10%), fish oil (3%), diamol (2%) and premix (1%). Partial replacement of dry matter of fishmeal, corn grain, wheat grain, wheat bran and fish oil by 20% and 40% of dry matter of duckweed, in a dry and fresh form, was performed. Diets of treatments 1 and 2 included 20% and 40% of duckweed, respectively, in a dry form. In treatments 3 and 4, tilapia received formulated diets 4 and 5 in addition to 20% and 40% fresh duckweed providing the same amount of dry matter and protein as in control. The specific growth rates (SGRs) of tilapia were 1.51+/-0.07, 1.38+/-0.03, 1.31+/-0.06, 1.44+/-0.02 and 1.33+/-0.05, in control and treatments 1-4. There was no significant difference between SGR for the control diet and the diet with 20% fresh duckweed, while the other treatment groups had significantly lower SGR. All the treatment diets provide good values for feed conversion ratios (FCRs) and protein efficiency ratio (PER). Dry matter of diets ranged from 61.8% in treatment 4 to 85.2% in control. All the diets have high PD (88.4-93.9%) and high-energy digestibility (78.1-90.7%). Dry matter of duckweed were 66.8, 63.3, 45.8 and 28.3 in treatments 1 to 4 respectively. Protein values were 78.4, 79.9, 77.6 and 75.9, while ED values were 59.8, 60.9, 64.5 and 58.4 in treatments 1 to 4 respectively. Analysis of body composition shows that tilapia fed diets with duckweed contain significantly (P
    Physico-chemical factors affecting the E.coli removal in a rotating biological contactor (RBC) treating UASB effluent
    Tafwik, A. ; Klapwijk, A. ; Buuren, J.C.L. van; El-Gohary, F. ; Lettinga, G. - \ 2004
    Water Research 38 (2004)5. - ISSN 0043-1354 - p. 1081 - 1088.
    waste stabilization ponds - bacterial die - water - transport - biofilms - survival - system
    The removal mechanism of E coli from UASB effluent using a Rotating Biological Contractor (RBC) has been investigated. Preliminary batch experiments in a RBC indicate a first-order removal kinetics. Variation in the dissolved oxygen concentration and E coli counts over the depth of the RBC has been recorded and indicates that the RBC is not a completely mixed reactor. Therefore batch experiments were carried out in a beaker where the different operating conditions can be controlled. Factors affecting the removal of E coli via a biofilm system as stirring, dissolved oxygen concentration, pH, and addition of cationic polymer were investigated, The results obtained indicated that the most important removal mechanism of E coli in the biofilm is the adsorption process, followed by sedimentation. Die-off is a relatively minor removal mechanism in an RBC system. Higher removal rate of E coli was observed in an aerobic compared to an anaerobic biofilm system. Variation of dissolved oxygen concentration (3.3-8.7 mg l(-1)) and pH-values between 6.5 and 9.3 did not exert any significant effect on the removal rate of the E coli by the heterotrophic biofilm. A rapid adsorption of E coli to the biofilm occurred during the first days after adding the cationic polymer, after which the adsorption slowed down. (C) 2003 Elsevier Ltd. 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.
    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
    Development of cost-effective reclamation technologies for domestic wastewater (CORETECH)
    Zeeman, G. ; Sanders, W. ; Fayyad, M. ; Khassab, G. ; El-Gohary, F. ; Al-Sa'ed, R. ; Angelakis, A. ; Lier, J.B. van - \ 2001
    In: Proceedings of EU INCO-MED Water Conference MEDAQAU Amman : MEDAQUA
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