Ranjan Sarukkalige

Polycyclic aromatic hydrocarbons (PAHs) removal by sorption: A review.

Polycyclic aromatic hydrocarbons (PAHs) are organic micro pollutants which are persistent compounds in the environment due to their hydrophobic nature. Concerns over their adverse effects in human health and environment have resulted in extensive studies on various types of PAHs removal methods. Sorption is one of the widely used methods as PAHs possess a great sorptive ability into the solid media and their low aqueous solubility property. Several adsorbent media such as activated carbon, biochar, modified clay minerals have been largely used to remove PAHs from aqueous solution and to immobilise PAHs in the contaminated soils. According to the past studies, very high removal efficiency could be achieved using the adsorbents such as removal efficiency of activated carbon, biochar and modified clay mineral were 100%, 98.6% and >99%, respectively. PAHs removal efficiency or adsorption/absorption capacity largely depends on several parameters such as particle size of the adsorbent, pH, temperature, solubility, salinity including the production process of adsorbents. Although many studies have been carried out to remove PAHs using the sorption process, the findings have not been consolidated which potentially hinder to get the correct information for future study and to design the sorption method to remove PAHs. Therefore, this paper summarized the adsorbent media which have been used to remove PAHs especially from aqueous solutions including the factor affecting the sorption process reported in 142 literature published between 1934 and 2015.

Surfactant-enhanced remediation of polycyclic aromatic hydrocarbons: A review

Polycyclic aromatic hydrocarbons (PAHs) are toxic, mutagenic and carcinogenic organic compounds that are widely present in the environment. The bioremediation of PAHs is an economical and environmentally friendly remediation technique, but it is limited because PAHs have low water solubility and fewer bioavailable properties. The solubility and bioavailability of PAHs can be increased by using surfactants to reduce surface tension and interfacial tension; this method is called surfactant-enhanced remediation (SER). The SER of PAHs is influenced by many factors such as the type and concentration of surfactants, PAH hydrophobicity, temperature, pH, salinity, dissolved organic matter and microbial community. Furthermore, as mixed micelles have a synergistic effect on PAH solubilisation, selecting the optimum ratio of mixed surfactants leads to effective PAH remediation. Although the use of surfactants inhibits microbial activities in some cases, this could be avoided by choosing an optimum combination of surfactants and a proper microbial community for the targeted PAH(s), resulting in up to 99.99% PAH removal. This article reviews the literature on SER of PAHs, including surfactant types, the synergistic effect of mixed micelles on PAH removal, the impact of surfactants on the PAH biodegradation process, factors affecting the SER process, and the mechanisms of surfactant-enhanced solubilisation of PAHs.

A bio-anodic filter facilitated entrapment, decomposition and in situ oxidation of algal biomass in wastewater effluent

This study examined for the first time the use of bioelectrochemical systems (BES) to entrap, decompose and oxidise fresh algal biomass from an algae-laden effluent. The experimental process consisted of a photobioreactor for a continuous production of the algal-laden effluent, and a two-chamber BES equipped with anodic graphite granules and carbon-felt to physically remove and oxidise algal biomass from the influent. Results showed that the BES filter could retain ca. 90% of the suspended solids (SS) loaded. A coulombic efficiency (CE) of 36.6% (based on particulate chemical oxygen demand (PCOD) removed) was achieved, which was consistent with the highest CEs of BES studies (operated in microbial fuel cell mode (MFC)) that included additional pre-treatment steps for algae hydrolysis. Overall, this study suggests that a filter type BES anode can effectively entrap, decompose and in situ oxidise algae without the need for a separate pre-treatment step.

Bioelectrochemical oxidation of organics by alkali-halotolerant anodophilic biofilm under nitrogen-deficient, alkaline and saline conditions

This work aimed to study the feasibility of using bioelectrochemical systems (BES) for organics removal under alkaline-saline and nitrogen (N) deficient conditions. Two BES inoculated with activated sludge were examined for organics (oxalate, acetate, formate) oxidation under alkaline-saline (pH 9.5, 25g/L NaCl) and N deficient conditions. One reactor (R1) received ammonium chloride as an N-source, while the other (R2) without. The reactors were initially loaded with only oxalate (25mM), but start-up was achieved only when acetate was added as co-substrate (5mM). Maximum current were R1: 908A/m3 (organic removal rate (ORR) 4.61kgCOD/m3·d) and R2: 540A/m3 (ORR 2.06kgCOD/m3·d). Formate was utilised by both anodic biofilms, but the inefficient oxalate removal was likely due to the paucity of microorganisms that catalyse decarboxylation of oxalate into formate. Further development of this promising technology for the treatment of alkaline-saline wastewater is warranted.

Evaluation of phosphorus adsorption capacity of various filter materials from aqueous solution

Rapid urbanisation has significantly increased the impervious surface along with increase in pollutants such as nutrients (nitrogen, phosphorus), sediments, oil, and hydrocarbon in stormwater. Their removal is important as they adversely affect the aquatic ecosystem and the environment. Thus, this study evaluated the performance of various adsorbent materials (red gum mulch, pine mulch, flyash, oyster shell, sawdust, clay, sand, zeolite, dolomite, alum and lime sludges) for the removal of phosphorus from synthetic stormwater. Among them, alum and lime sludges appeared to be the most effective in removing phosphorus. Further analysis showed that alum and lime sludges remove 99 and 90% phosphorus within 60 minutes from the synthetic stormwater. Therefore, this study demonstrates that the lime and alum sludges could be highly useful as a sustainable and cheap filter media for stormwater treatment systems that are enriched in phosphorus.

Assessing the suitability of sediment-type bioelectrochemical systems for organic matter removal from municipal wastewater: a column study

This study examines the use of bioelectrochemical systems (BES) as an alternative to rock filters for polishing wastewater stabilisation ponds (WSPs) effluent, which often contains soluble chemical oxygen demand (SCOD) and suspended solids mainly as algal biomass. A filter type sediment BES configuration with graphite granules (as the surrogate for rocks in a rock filter) was examined. Three reactor columns were set up to examine three different treatments: (i) open-circuit without current generation; (ii) close-circuit - with current generation; and (iii) control reactor without electrode material. All columns were continuously operated for 170 days with real municipal wastewater at a hydraulic retention time of 5 days. Compared to the control reactor, the two experimental reactors showed significant improvement of SCOD removal (from approximately 25% to 66%) possibly due to retention of biomass on the graphite media. However, substantial amount of SCOD (60%) was removed via non-current generation pathways, and a very low Coulombic efficiency (6%) was recorded due to a poor cathodic oxygen reduction kinetics and a large electrode spacing. Addressing these challenges are imperative to further develop BES technology for WSP effluent treatment.

Rapid start-up of a bioelectrochemical system under alkaline and saline conditions for efficient oxalate removal

This study examined a new approach for starting up a bioelectrochemical system (BES) for oxalate removal from an alkaline (pH > 12) and saline (NaCl 25 g/L) liquor. An oxalotrophic biofilm pre-grown aerobically onto granular graphite carriers was used directly as both the microbial inoculum and the BES anode. At anode potential of +200 mV (Ag/AgCl) the biofilm readily switched from using oxygen to graphite as sole electron acceptor for oxalate oxidation. BES performance was characterised at various hydraulic retention times (HRTs, 3-24 h), anode potentials (-600 to +200 mV vs. Ag/AgCl) and influent oxalate (25 mM) to acetate (0-30 mM) ratios. Maximum current density recorded was 363 A/m3 at 3 h HRT with a high coulombic efficiency (CE) of 70%. The biofilm could concurrently degrade acetate and oxalate (CE 80%) without apparent preference towards acetate. Pyro-sequencing analysis revealed that known oxalate degraders Oxalobacteraceae became abundant signifying their role in this novel bioprocess.