Simulation study of a practical approach to enhance cadmium removal via biological treatment by controlling the concentration of MLSS.

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.

Simulate permeable reactive barrier by using a COMSOL model and comparison with the Thomas, Yoon-Nelson and Clark models for CR dye remediation by composite adsorbent (sewage and waterworks sludge).

The remediation of Congo Red (CR) dye by the synthetic sorbent composited from sewage and waterworks sludge was studied in batch and continuous experiments. The continuous experiments studied the composite synthetic after mixing with composite synthetic sorbent filter (CSF) glass waste to increase the hydraulic conductivity of the permeable reactive barrier (PRB). The synthetic composite sorbent was characterised by the nitrogen adsorption-desorption tests, field emission-scanning electron microscopy and X-ray diffraction. For evaluating the batch tests, the variable conditions of initial concentration, solution pH, agitation time and agitation speed were studied. The synthetic sorbent showed a high ability to remove the CR from a contaminated water, with maximum sorbent uptake equal to 9,469.211 mg/g and composite adsorbent-filter CSF equal to 4,415.946 mg/g. Pseudo-second-order kinetic model and Langmuir isotherm model governed the adsorption process. The column tests showed the highest reactivity, with 50:50 weight ratios of the adsorbent to filter glass waste. The experiments were done with different concentrations of CR and different bed heights of CSF as the PRB for 90 days. There was a delay in the breakthrough time when decreasing the contaminant concentrations and when increasing the composite adsorbent-filter CSF bed height. The breakthrough curves were well represented by the COMSOL model.

Synthesis of composite sorbent for the treatment of aqueous solutions contaminated with methylene blue dye.

To apply the principles of sustainability, this study aims to prepare the composite sorbent from mixing of solid wastes that resulted from activities of treatment plants for wastewater and water supply. The manufacturing process depends on the mixing of sewage sludge with waterworks sludge at different proportions and the best mixture is modified by ferric nitrate solution. The prepared composite sorbent was evaluated as permeable reactive barrier (PRB) in the capturing of methylene blue (MB) dye presented in the simulated groundwater. Results proved that the suitable mixture of composite sorbent consisting of 0.25 g sewage sludge with 0.75 g waterworks sludge coated with aqueous solution of 2 g of Fe(NO3)2 achieved the maximum sorption capacity. In comparison with Freundlich model, Langmuir expression described the sorption measurements in a well manner; so, the chemisorption is governed by the removal of MB with maximum adsorption capacity reached to 268.98 mg/g. Kinetic measurements could be more representative by pseudo-first-order model and this means that the sorption process is supported by physical forces. Finally, the effects of inlet concentrations and bed thickness on the migration of MB front were simulated in an efficient manner by COMSOL Multiphysics 3.5a package with root mean squared errors not in excess of 0.152.