Adsorption of lead, copper and zinc in a multi-metal aqueous solution by waste rubber tires for the design of single batch adsorber.

Heavy metal pollution has emerged as one of the most serious environmental challenges facing the world today. The removal of heavy metals from the effluent is of special environmental concern because of their toxicity and persistence in nature. This study presents the suitability of activated carbon from waste rubber tire as a low-cost adsorbent for multiple adsorption of copper, lead and zinc from wastewater. The adsorbent removed heavy metal ions effectively from solution medium in the order of copper > lead > Zinc. The adsorption process was rapid with all metals reaching equilibrium within 120 min. The optimum pH for Lead was achieved at 5 and 6 for copper and Zinc. The removal of heavy metals was discovered to increase with adsorbent dosage and contact time and reduced with initial concentration. The adsorption of multiple heavy metals was modeled using Freundlich and Langmuir adsorption isotherms to assess the experimental findings. The equilibrium data better fitted to the Langmuir isotherm with regression coefficient (R2) of 0.9831, 0.9992 and 0.9953 for lead, copper and zinc respectively. The maximum adsorption capacities (Qmax) at equilibrium were 9.6805 mg/g, 12.4378 mg/g and 4.9950 mg/g for Lead, Copper and Zinc respectively. The adsorption kinetics indicated that pseudo-second-order kinetic model described well the sorption mechanism for multiple adsorption of heavy metals with R2 of more than 0.99 for all metal ions. An empirical model for predicting and designing of a single batch adsorber for 95 % multiple heavy metal ion removal at any given initial heavy metal ion concentration and effluent volume was further developed using activated carbon from waste rubber tires. Waste rubber tire Activated carbon demonstrated an ability for the treatment of wastewater containing these heavy metals in multimetal solutions.

Simulation of batch-operated experimental wetland mesocosms in AQUASIM biofilm reactor compartment.

In this study, a mathematical biofilm reactor model based on the structure of the Constructed Wetland Model No.1 (CWM1) coupled to AQUASIM's biofilm reactor compartment has been used to reproduce the sequence of transformation and degradation of organic matter, nitrogen and sulphur observed in a set of constructed wetland mesocosms and to elucidate the development over time of microbial species as well as the biofilm thickness of a multispecies bacterial biofilm in a subsurface constructed wetland. Experimental data from 16 wetland mesocosms operated under greenhouse conditions, planted with three different plant species (Typha latifolia, Carex rostrata, Schoenoplectus acutus) and an unplanted control were used in the calibration of this mechanistic model. Within the mesocosms, a thin (predominantly anaerobic) biofilm was simulated with an initial thickness of 49 µm (average) and in which no concentration gradients developed. The biofilm density and area, and the distribution of the microbial species within the biofilm were evaluated to be the most sensitive biofilm properties; while the substrate diffusion limitations were not significantly sensitive to influence the bulk volume concentrations. The simulated biofilm density ranging between 105,000 and 153,000 gCOD/m(3) in the mesocosms was observed to vary with temperature, the presence as well as the species of macrophyte. The biofilm modeling was found to be a better tool than the suspended bacterial modeling approach to show the influence of the rhizosphere configuration on the performance of the constructed wetlands.

Performance comparison and economics analysis of waste stabilization ponds and horizontal subsurface flow constructed wetlands treating domestic wastewater: a case study of the Juja sewage treatment works.

The performance, effluent quality, land area requirement, investment and operation costs of a full-scale waste stabilization pond (WSP) and a pilot scale horizontal subsurface flow constructed wetland (HSSF-CW) at Jomo Kenyatta University of Agriculture and Technology (JKUAT) were investigated between November 2010 to January 2011. Both systems gave comparable medium to high levels of organic matter and suspended solids removal. However, the WSP showed a better removal for Total Phosphorus (TP) and Ammonium (NH4(+)-N). Based on the population equivalent calculations, the land area requirement per person equivalent of the WSP system was 3 times the area that would be required for the HSSF-CW to treat the same amount of wastewater. The total annual cost estimates consisting of capital, operation and maintenance (O&M) costs were comparable for both systems. However, the evaluation of the capital cost of either system showed that it is largely influenced by the size of the population served, local cost of land and the construction materials involved. Hence, one can select either system in terms of treatment efficiency. When land is available other factor including the volume of wastewater or the investment, and O&M costs determine the technology selection.