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The water separated by sludge treatment processes is known as the sidestreams, such as the centrate, underflow belt thickener, and supernatant gravity thickener. The sidestreams have significant amounts of contaminants, particularly nutrients, and are returned to the wastewater treatment plant head. Returning the sidestreams to the head of the plant causes both technical and financial problems. This paper models the effect of sidestreams on the treatment of mainstream in full-scale conventional activated sludge systems operated with anaerobic/anoxic/oxic (A2/O). The effects of sidestreams nutrients and inert materials, the pollutants fate in the A2/O system, oxygen consumed, and energy required by sidestreams are modeled using GPS-X8 simulation. The results showed that the discharge ratio of the sidestreams to the mainstream is 4 %. The proportion of the pollutants present in the sidestream to the mainstream were 4.3 %, 4.7 %, 8.8 %, 21 %, 40 %, and 11 % for BOD, COD, TSS, NH4, PO4, and H2S, respectively. The GPS-X model showed that high orthophosphate and hydrogen sulfide concentrations were seen in the anaerobic zone. While all other pollutants begin to decay, phosphates and hydrogen sulfide gas also begin to decrease gradually in anoxic and oxic zones, noting the high concentrations of nitrates and sulfates in the oxic zone. An added 10 % of oxygen is needed for the sidestreams ammonia oxidation, which is more than the amount needed for the oxidation of BOD. The percentage of alkali used to improve the nitrification process due to the ammonia in the sidestreams was 30 % of the specified amount of ammonia in the mainstream. This study proved that the plant's sidestreams adversely increased oxygen, energy, and alkali consumption.

Abstract The fate of cadmium at the Muharram Aisha wastewater treatment plant in Karbala governorate, Iraq was studied using the TOXCHEM model. Cadmium, a known carcinogen, and is considered one of the most dangerous heavy metals and high concentrations, greater than permissible limits, were found in the treated wastewater. The plant operates using an activated sludge system and this was modeled via TOXCHEM with a sensitivity analysis carried out on the extended aeration system. Prior to analysis, the model was calibrated and validated for cadmium, with the adjustments leading to a mean square error (RMSE) and correlation coefficient (R) of 0.0001 and 0.81, respectively. The mass balance of cadmium in the Muharram Aisha treatment plant was found to be 4832.44 g/day (37.1726%) in the treated wastewater and 8164.52 g/day (62.804%) in the sludge, which indicated that the mix liquor suspended solid (MLSS) was the most sensitive factor. The sensitivity to cadmium was analyzed via MLSS in the extended aeration system and the results o indicated that the higher the MLSS concentration (mg/L), the greater the removal of cadmium in the treated wastewater. It was found that increasing the MLSS through a biological treatment method reduced the concentration of cadmium without the need for additional of any (potentially harmful) chemical treatments. The plant was subsequently operated for a period of 5 months with the MLSS increased from 1500 to 4500 mg/L, and this reduced the concentration of cadmium in the wastewater from 0.36 to 0.01 mg/L as a consequence. This research demonstrates how the novel application of TOXCHEM can be a useful tool in the reduction of heavy metal contamination in the environment.

H2S is one of the principal odor gases released from sewer networks and understanding the rate of H2S release into sewer air space and ventilation to the atmosphere is crucial for preventing or minimizing odor and corrosion issues in sewer systems. TOXCHEM model was used to simulate the fate of H2S gas in roads for this study. The model was calibrated for the spring and summer seasons and validated for the remainder of the seasons. The predicted behavior showed good correlation to measurements on real samples following statistical analysis, with R2, R, and RMSE results between (0.93–0.97), (0.8–0.82), and (0.000438–0.000838), respectively. A sensitivity study was performed to assess the effect of various pH values, drop heights, tailwater depths, stream widths, and sewer ventilation rate levels. The results showed that the emissions concentrations for winter, spring, summer, and autumn reached 3500, 5044, 6425, and 4045 ppm respectively. All the emissions levels from this DS can be considered hazardous, and this was particularly evident during the summer months. This study has helped to clarify the fate and emission of hydrogen sulfide gas at the DS by simulation using a TOXCHEM model. HIGHLIGHTS The drop structure can substantially increase the emission of hydrogen sulfide from the liquid phase to the air phase.; Discussion of the most important factors that contribute to the emission of H2S gas in the drop structures.; Determination of the amount of hydrogen sulfide gas emission in the sulfate-rich wastewater.; The use of the TOXCHEM model to simulate the emission of hydrogen sulfide gas in the drop structure.;

Worldwide, most treatment systems are retuning sidestreams to the wastewater treatment plant head without treatment. This study established an innovative process to separately treat all sidestream lines (supernatant gravity thickener, underflow mechanical thickener, and centrate) away from plant mainstream and return treated sidestream effluents to plant wastewater outfall instead of wastewater head. It aims to start up and operate a novel EN-MBBR to eliminate sidestreams impacts on a full-scale A2/O sewage treatment plant. The effects of DO, RAS, and media portion on the reactor were modeled using GPS-X. The system successfully started and reached a steady-state in 28 days. The pilot system processed 30 m3/d of the sidestreams, and the average of 8 months effluent concentrations for COD, BOD, TSS, PO4, NH4, NO2, NO3, H2S were 55, 4, 11, 0.16, 0.2, 0.17, 100, and 0.11 mg/L, respectively. Adding 3 kg/day of calcium hydroxide contributed to improving the nitrification process and reducing phosphates from 40 mg/L to 0.16 mg/L, but it caused an initial shock to the system that lasted more than a week, and then it was stabilized. Modeling results showed that DO concentrations affected the nitrification process but stabilized at a concentration of 3 mg/L. When operating the EN-MBBR as an EN-IFAS system, the RAS has positively contributed to reducing sludge in this system, whereas the sludge proportion is reduced by 60%. The media portion had a significant effect on the removal of nutrients, as it gave the best results when the rate of reactor filling with carriers was between 40 and 50%.

The emission and fate of methyl mercaptan from the residential complex treatment plant (RCTP) moving bed bioreactor (MBBR) process in the city of Al-Hur in Karbala governorate in Iraq were studied using the TOXCHEM 4.1 model. The release of odorous sulfur compounds from treatment plants harms workers and the surrounding area. Methyl mercaptan, in particular, is responsible for odors similar to rotten cabbage. The sensitivity analysis for the methyl compounds in the MBBR system was conducted based on the following factors: a large thick biofilm layer, the specific surface area of media, media fill fraction, and aeration flowrate. The model was validated via RMSE and R, which showed the model outputs are representatives of real-world observations. Degradation and emission were shown to be the two most important processes in the system. During the summer (32 °C) and winter (12 °C), about 13 and 10%, 2 and 4%, 0.5 and 1%, and 85 and 85% were emitted into the atmosphere, discharged with effluent, sorbed into sludge, and biodegraded, respectively. The overall concentrations of CH4S emitted in summer and winter were 1.78 and 1.38 ppm, respectively. Operating the MBBR system with a thick biofilm layer, a large specific surface area of media, a greater media fill fraction, and a low aeration rate contributed significantly to the decomposition of methyl mercaptan and thus decreased emission into the atmosphere. Finally, the TOXCHEM simulation accurately predicts the fate of CH4S and the emissions inherent to the MBBR system. The manipulation of the operating factors led to the improvement of the system and the reduction of methyl mercaptan gas emissions without the need to add units and chemical additives. HIGHLIGHTS The methyl mercaptan emitted by a full-scale MBBR WWTP was studied.; Aeration tank and equalization basin emitted the highest CH4S concentrations.; TOXCHEM modeling was used to calculate the distribution of CH4S around the WWTP.; CH4S concentrations exceeded the threshold limit at this plant.; CH4S emission was affected by the following three main factors: biodegradation, absorption by the sludge, and stripping.;

Abstract The novel process consisted of two steps was established by combining all sidestreams lines (supernatant gravity thickener, underflow mechanical thickener, and centrate), treating them together away from the mainstream treatment plant, and returning treated sidestreams effluents to the plant outfall instead of plant head. The two steps novelty treatment combined degradation, nitrification, and dilution processes. To treat combined sidestreams, a novel pilot extended nutrient moving bed biofilm reactor was developed. The effects of sidestream elimination on a full-scale anaerobic/anoxic/oxic system were simulated using GPS-X7. The statistical results of R values greater than 0.8 and NMSE values near zero proved the calibrated model’s validation. The novel system successfully removed 98, 93, 100, 85, 98, 100, and 98% of BOD, COD, NH4, NO3, TSS, H2S, and PO4-P from sidestreams, respectively. Furthermore, the simulation results showed that eliminating sidestreams has reduced volumes of full-scale A2/O facilities, controlled hydraulic and pollutants shocks, and minimized cost and energy. The novel process proved successful in treating combined sidestreams and eliminating their impacts on the A/O2 system.

Abstract Odors due to the emission of hydrogen sulfide (H2S) have been a concern in the sewage treatment plants over the last decades. H2S fate and emissions from extended aeration activated sludge (EAAS) system in Muharram Aisha-sewage treatment plant (MA-STP) were studied using TOXCHEM model. Sensitivity analysis at different aeration flowrate, H2S loading rate, wastewater pH, wastewater temperature and wind speed were studied. The predicted data were validated against actual results, where all the data were validated within the limits, and the statistical evaluation of normalized mean square error (NMSE), geometric variance (VG), and correlation coefficient (R) were close to the ideal fit. The results showed that the major processes occurring in the system were degradation and emission. During summer (27 °C) and winter (12 °C), about 25 and 23%, 1 and 2%, 2 and 2%, and 72 and 73% were fated as emitted to air, discharged with effluent, sorbed to sludge, and biodegraded, respectively. At summer and winter, the total emitted concentrations of H2S were 6.403 and 5.614 ppm, respectively. The sensitivity results indicated that aeration flowrate, H2S loading rate and wastewater pH highly influenced the emission and degradation of H2S processes compared to wastewater temperature and wind speed. To conclude, TOXCHEM model successfully predicted the H2S fate and emissions in EAAS system.

ABSTRACT The research aims at calculating the economic feasibility of honey production by choosing a random sample of beekeeping project in Abu- Ghraib. The questionnaire data concern the production season 2011. The results showed that all criteria for the calculation of economic feasibility, which were applied on research sample, were profitable. The results also showed that fixed costs consisted about 84% while the variable costs consisted 16% of total costs. The results of the revenues for bee-keeping project in the sample showed that the net profit was ID (9692000), This was due to the large revenues in comparison with low costs which is consistent with economic logic. The revenue of each invested dinar was (4.33) dinars which expresses the good economic feasibility. The project management recovered the invested capital in three months period when the pay-back period criteria was applied which indicates the very short period in comparison with the pay-back period of other projects .