Prof. Dr. Abdelsalam Elawwad (أ.د. عبد السلام العواد)

A pilot plant consisting of a combined up-flow anaerobic sludge blanket (UASB) and a continuous flow sequencing batch reactor (cSBR) was tested for treating domestic wastewater. After the start-up, the system was operated for 115 days at a retention time of 5.7 h in the UASB reactor and a cycle time of 8 h in the cSBR. The efficiency of the removal of the average chemical oxygen demand (COD) and the total suspended solids (TSS) in the UASB reactor were 48% and 46%, respectively. The overall average removal efficiencies for the COD, TSS, and ammonia in the system were 85%, 87%, and 82%, respectively. The system was optimized for sludge production and tested for approximately 120 days for sludge cycling between the cSBR and the inlet of the UASB. In comparison to sludge production at a solids retention time of 8.6 days, the implementation of this strategy resulted in an average 89% reduction in sludge production and a 32% increase in biogas production. No effect on the removal efficiencies of COD, TSS, and ammonia was seen during the sludge cycling process, which ran for more than 4 months. The findings indicate that the scheme proposed in this study could be a promising, cost-effective option for wastewater treatment in small communities and decentralized systems.

In developing countries, and due to the high cost of treatment of industrial wastewater, municipal wastewater treatment facilities usually receive a mixture of municipal wastewater and partially treated industrial wastewater. As a result, an increased potential of shock loads with high pollutant concentration is expected. The use of mathematical modelling of wastewater treatment is highly efficient in such cases. A dynamic model based on ASM3 describing the performance of the activated sludge process at a full scale wastewater treatment plant (WWTP) receiving mixed domestic–industrial wastewater located in an arid area is presented. ASM3 was extended by adding the Arrhenius equation to respond to changes in temperature. BioWin software V.4 was used as the model platform. The model was calibrated under steady-state conditions, adjusting only three kinetic and stoichiometric parameters: maximum heterotrophic growth rate (μH = 8 d−1), heterotrophic aerobic decay rate (bH, O2 = 0.18 d−1), and aerobic heterotrophic yield (YH,O2 = 0.4 (gCOD/gCOD)). ASM3 was successful in predicting the WWTP performance, as the model was validated with 10 months of routine daily measurements. ASM3 extended with the Arrhenius equation could be helpful in the design and operation of WWTPs with mixed municipal–industrial influent in arid area.

In this study, the feasibility of utilizing an algal photo-bioreactor as a polishing step for secondary treated wastewater was tested. Algal photo-bioreactors utilize the interaction of bacteria and microalgae, which offers an eco-friendly and lower energy consumption technology for nutrient removal and biomass production. The pilot plant in this study consists of an algal photo-bioreactor with an effective volume of 0.188 m3 and a lamella settler, constructed and operated at Zenin Wastewater Treatment Plant, Giza, Egypt. The pilot plant was operated for about 112 days under continuous flow conditions at ambient temperature. The effect of hydraulic retention time (HRT) on the rate of removal of organics and nutrients was investigated at a fixed solid retention time of 15 days. The photo-bioreactor was continuously illuminated with light obtained during the day from sunlight and at night from incandescent lamps. HRT of 16.1 hours had the best overall organic and nutrient removal efficiency. However, from an economic standpoint, the optimum applied load was 50 g N/d/m3 and 22 g P/d/m3 for ammonia and phosphorus, respectively. These applied loads correspond to HRTs in the range of 5 to 6 hours and expected removal efficiencies above 85% and 70%, respectively, for ammonia and phosphorus.

An integrated system that combines an up-flow anaerobic sludge blanket (UASB) and a continuous-flow sequencing batch reactor (CSBR) was tested for treating medium-strength domestic wastewater. CSBR requires less control and is simple compared to conventional SBR, which is an important advantage in small and decentralized areas. After the start-up, the system was operated for 115 days at a retention time of 5.7 h in the UASB reactor and a cycle time of 8 h in the CSBR. The average chemical oxygen demand (COD) and total suspended solids (TSS) removal efficiencies in the UASB reactor were 48% and 46% respectively. The overall average removal efficiencies for COD, TSS and ammonia in the system were 85%, 87%, and 82%, respectively. Then, the system optimized for excess sludge production. For that reason, the system was tested for about 120 days for sludge recycling to the inlet of the UASB. By implementing this strategy, a 75% reduction in sludge production and a 35% increase in biogas production were achieved. There was no effect on the removal efficiencies of COD, TSS, and NH4 during the sludge recycling process that was performed for over 4 months. The findings indicate that the proposed scheme in this study could be a promising and cost-effective option for decentralized wastewater treatment and wastewater generation in small communities.

The BioWin general activated sludge (AS) model (EnviroSim Associates, Ltd, Canada) was extended to predict the kinetics of phenol and cyanide removal from coke-oven wastewater mixed with sewage. To apply the modeling for this type of wastewater, a different model structure and an accurate estimation of the stoichiometric and kinetic parameters are required. In this study, additional processes for the phenol and cyanide were added to the BioWin AS model. Due to the inhibitory effect phenol and cyanide have on biological processes, the Haldane equation was used rather than the Monod equation that is typically used in wastewater modeling. A sensitivity analysis was performed to select the most sensitive parameter in the extended model. The model was calibrated under steady-state conditions and validated under dynamic-flow conditions. Adjustments were made only to the most sensitive parameters of the extended model processes related to phenol and cyanide. The new calibrated parameters were compared to the existing parameters from the literature, which were based on batch lab-scale experiments with synthetic wastewater. The extended model was capable of describing COD, ammonium, phenol, and cyanide removal in a full-scale coke-oven wastewater treatment plant under dynamic conditions.

The conventional gravity sewer is the most commonly used rural sewerage system in developing countries. However, this system has many technical, economic, environmental, and social disadvantages. Vacuum sewers could serve as a good competitor as an alternative system to conventional gravity sewers. A sample of 33 rural villages with populations of <10,000 people is selected from Egypt. A statistical analysis was done using SPSS and STATISTICA software where population and area variables had the most significant effect on the calculation of investment, operation, and maintenance costs. It was found that investment costs for the vacuum system were mostly lower than for the conventional one, while operational and maintenance costs played significant roles. Prediction models were obtained based on multiple quadratic regression models. It was found that the vacuum system was economically competitive in large villages with low population densities. Environmentally and socially, the vacuum sewers proved to be better than gravity sewers.

Leakage in sewerage system can cause groundwater and soil contamination in urban areas, especially in area with a high groundwater table. This is a serious problem in small agricultural villages which rely on ground water as a source for irrigation and drinking purposes. In the developed countries, the recent trend in areas with low population densities is using vacuum sewerage system. Vacuum system could be environmentally safer than conventional gravity system, protecting public health, preventing exfiltration to the ground water, very easily applied in a relatively short time, and can cope with a faster expansion of the urbanized areas. Detailed hydraulic design were held for both gravity sewer and vacuum sewer systems in 28 Egyptian agricultural villages as a case study for developing regions. Different conditions, such as population, areas, and terrain slopes were evaluated. Cost comparisons based on statistical analysis were done to assess the feasibility of using vacuum sewerage in developing regions. Based on this study, from financial point of view, vacuum sewerage system was a good competitor to conventional systems in flat areas and areas with high groundwater table. From the environmental point of view, it is recommended to construct the vacuum sewerage system in such agricultural villages. The local market supplying of the construction equipment especially collection chambers will greatly affect the investment cost. Capacity building and social mobilization will also play a great role in sustainability of this system.

The effectiveness of three operational strategies for maintaining nitrifiers in bench-scale, aerated, submerged fixed-bed biofilm reactors (SFBBRs) during long-term starvation at 20°C were evaluated. The operational strategies were characterized by the resulting oxidation-reduction potential (ORP) in the SFBBRs. The activity rates of the nitrifiers were measured and the activity decay was expressed by half-life times. It was found that anoxic and alternating anoxic/aerobic conditions were the best ways to preserve ammonia-oxidizing bacteria (AOB) during long starvation periods and resulted in half-life times of up to 34 and 28 days, respectively. Extended anaerobic conditions caused the half-life for AOB to decrease to 21 days. In comparison, the activity decay of nitrite-oxidizing bacteria (NOB) tended to be slightly faster. The activity of AOB biofilms that were kept for 97 days under anoxic conditions could be completely recovered in less than one week, while over 4 weeks was needed for AOB kept under anaerobic conditions. NOB were more sensitive to starvation and required longer recovery periods than AOB. For complete recovery, NOB needed approximately 7 weeks, regardless of the starvation conditions applied. Using the fluorescence in situ hybridization (FISH) technique, Nitrospira was detected as the dominant NOB genus. Among the AOB, the terminal restriction fragment length polymorphism (TRFLP) technique showed that during starvation and recovery periods, the relative frequency of species shifted to Nitrosomonas europaea/eutropha, regardless of the starvation condition. The consequences of these findings for the operation of SFBBRs under low-load and starvation conditions are discussed.

The effects of two different start-up regimes on the operation performance and population dynamics of nitrification were evaluated in aerated submerged fixed-bed biofilm reactors (SFBBRs) operated at 20 °C on a medium-strength ammonium wastewater at the bench scale. The reactors were operated in parallel at start-up with two reactors under the maximum nitrogen loading rate condition (NLR) designed for the system, and for the other two reactors, the NLR was increased stepwise over a period of 22 days. The dominant microorganism among the ammonia-oxidising bacteria (AOB) in the seeding sludge was Nitrosomonas oligotropha. There was an observed growth of Nitrosospira and Nitrosomonas europaea/eutropha when the reactors were started up. Nitrosospira vanished during the course of reactor operations, while N. communis was observed to flourish in the second low-load stage of the SFBBR cascade. Nitrospira was the dominant nitrite-oxidising bacteria (NOB) genus present throughout the investigation. Reactors gradually loaded showed higher nitrification rates during the start-up. However, there was no significant difference in the total time required to reach steady state between the two start-up regimes. The AOB required 30 days and the NOB required an additional 8 days on average to reach steady state because NOB development was inhibited by free ammonia (FA). Proposals with respect to pH control, seeding sludge and sludge recycling were developed to shorten the start-up period in SFBBRs. The specific nitrification rates of the attached biomass in SFBBRs were compared to previous studies as well. The results from these experiments will aid in process design.

Huge amounts of alum sludge are generated by water treatment plants every day. The common disposal system of alum sludge in Egypt is to discharge it into the nearest waterways. The impact of aluminum toxicity released from sludge on aquatic life has become a significant environmental issue. Re-use of alum sludge in wastewater treatment may provide a solution for issues related to sludge disposal. It may also help to increase the performance of existing WWTPs, because that alum sludge contains a large portion of insoluble aluminum hydroxides that can be utilized as a coagulant in the wastewater settling processes. Therefore, this paper attempted to study the effect of alum sludge addition on primary and secondary wastewater settling processes. Also, effect of alum sludge addition on the characteristics of the settled primary and secondary wastewater sludge was investigated. Alum sludge and wastewater samples were applied to a series of Jar test experiments. Re-use of alum sludge achieved highly removal efficiency values for the primary and secondary settling processes. The volume of primary settled sludge increased and moisture content slightly increased. However, alum sludge found to have a slight effect on the using of sludge as fertilizer. Finally, SVI values for secondary precipitated sludge decreased, which can solve the problems related to bulking in the secondary settling tanks.