Sewage Sludge ZnCl2-Activated Carbon Intercalated MgFe-LDH Nanocomposites: Insight of the Sorption Mechanism of Improved Removal of Phenol from Water.

Keywords: sludge-activated carbon; MgFe layered double hydroxide; nanocomposite materials; phenol aqueous uptake; mechanistic studies; reusability performance.

Polyaspartate extraction of cadmium ions from contaminated soil: Evaluation and optimization using central composite design.

The occurrences of heavy metal contaminated sites and soils and the need for devising environmentally friendly solutions have become global issues of serious concern. In this study, polyaspartate (a highly biodegradable agent) was synthesized using L-Aspartic acid via a new modified thermal procedure and employed for extraction of cadmium ions (Cd) from contaminated soil. Response surface methodology approach using 35 full faced centered central composite design was employed for modeling, evaluating and optimizing the influence of polyaspartate concentration (36-145mM), polyaspartate/soil ratio (5-25), initial heavy metal concentration (100-500mg/kg), initial pH (3-6) and extraction time (6-24h) on Cd ions extracted into the polyaspartate solution and its residual concentration in the treated soil. The Cd extraction efficacy obtained reached up to 98.8%. Increase in Cd extraction efficiency was associated with increase in the polyaspartate and Cd concentration coupled with lower polyaspertate/soil ratio and initial pH. Under the optimal conditions characterized with minimal utilization of the polyaspartate and high Cd ions removal, the extractible Cd in the polyaspartate solution reached up to 84.4mg/L which yielded 85% Cd extraction efficacy. This study demonstrates the suitability of using polyaspartate as an effective environmentally friendly chelating agent for Cd extraction from contaminated soils.

Removal of Phenolic Compounds from Water Using Sewage Sludge-Based Activated Carbon Adsorption: A Review.

Due to their industrial relevance, phenolic compounds (PC) are amongst the most common organic pollutants found in many industrial wastewater effluents. The potential detrimental health and environmental impacts of PC necessitate their removal from wastewater to meet regulatory discharge standards to ensure meeting sustainable development goals. In recent decades, one of the promising, cost-effective and environmentally benign techniques for removal of PC from water streams has been adsorption onto sewage sludge (SS)-based activated carbon (SBAC). This is attributed to the excellent adsorptive characteristics of SBAC and also because the approach serves as a strategy for sustainable management of huge quantities of different types of SS that are in continual production globally. This paper reviews conversion of SS into activated carbons and their utilization for the removal of PC from water streams. Wide ranges of topics which include SBAC production processes, physicochemical characteristics of SBAC, factors affecting PC adsorption onto SBAC and their uptake mechanisms as well as the regeneration potential of spent SBAC are covered. Although chemical activation techniques produce better SBAC, yet more research work is needed to harness advances in material science to improve the functional groups and textural properties of SBAC as well as the low performance of physical activation methods. Studies focusing on PC adsorptive performance on SBAC using continuous mode (that are more relevant for industrial applications) in both single and multi-pollutant aqueous systems to cover wide range of PC are needed. Also, the potentials of different techniques for regeneration of spent SBAC used for adsorption of PC need to be assessed in relation to overall economic evaluation within realm of environmental sustainability using life cycle assessment.

Treatment and kinetic study of cyanobacterial toxin by ozone.

A rapid scan-stopped flow (RS-SF) reactor was used to study reaction between ozone and cyanobacterial toxins [microcystin-LR (MC-LR) and microcystin-RR (MC-RR)] at different pH values and over a temperature range of 20-30 degrees C. The ozonation reaction was very effective for elimination of microcystin; solutions of concentration up to 5 mg/L MC-LR were totally oxidized by an ozone dosage of 2 mg/L. Reactions were dependent on ozone dose, temperatures, and pH. A more effective reaction took place at a higher ozone dose, higher temperatures, and more acidic pH. Spectrophotometer analysis was used to study the ozonation kinetics. Reactions were very fast: with an initial ozone concentration of 2 mg/L the half-life time of the toxins was less than 20 s. Ozonation reaction was successfully modeled to an overall second-order kinetics and with first-order kinetics for both ozone and toxins. Overall rate constants (K) were found to be 6.79 x 10(4) M(-1)s(-1) for MC-LR and 2.45 x 10(5) M(-1)s(-1) for MC-RR at 20 degrees C, with a pH of 2. The main degradation intermediates and the toxicity of the treated solution were also evaluated. The identified by-products were related to ozone dose. The high available ozone concentration degraded the toxins into smaller by-products and led to a ring opening. On the other hand, at a low ozone dose larger intermediates were detected. The treated solution toxicity was also found to be related to the ozone available in the aqueous solution; a high ozone dose led to cleavage of the Adda side chain from the toxin and reduced the toxicity.

Solar/UV-induced photocatalytic degradation of volatile toluene.

The degradations of gaseous toluene (2-20 ppmv) by solar irradiation (solar), solar irradiation and ozone (solar + O3), solar photocatalytic reaction (solar + TiO2) and solar photocatalytic reaction in the presence of ozone (solar + O3 + TiO2) were studied in a pilot plant. The effects of the inlet concentration of toluene, flow rate and relative humidity on the decomposition of toluene were followed. The experimental results showed that the solar process alone did not eliminate a significant amount of toluene. However, the combination of solar irradiation with either O3 or TiO2 improved the decomposition rate of toluene. A significant toluene conversion, at a high toluene inlet concentration, was achieved by the solar + O3 + TiO2 process. Toluene decomposition was found to be affected by the inlet flow rate; a high flow rate resulted in low conversion. The solar + O3 process was found to be more affected by gas relative humidity; the optimal humidity was found to be around 50%. The products from the photo-degradation of toluene were found to be water-soluble organics. The water-soluble organics were found to have high biodegradability. Thus, a post treatment consisting of a washing technique followed by biological treatment can be proposed.