Adsorption of arsenic from water using activated neutralized red mud.

In this paper activated seawater-neutralized red mud, herein referred to as activated Bauxsol (AB), is used as a novel adsorbent for removing inorganic arsenic (As) from water. The adsorption of As onto AB is studied as a function of contact time, particle size, pH, initial As concentration, AB dosage, and temperature. Kinetic data indicate that the process pseudoequilibrates in 3 and 6 h for As(V) (arsenate) and As(III) (arsenite), respectively, and follows a pseudo-first-order rate expression. Within the range tested, the optimal pH for As(V) adsorption is 4.5, and close to 100% removal can be achieved irrespective of the initial As(V) concentration. Desorption of As(V) is greatest at pH 11.6 where a maximum of 40% can be achieved. In contrast, the optimum pH for As(III) removal is 8.5, and the removal efficiency changes with the initial As(III) concentration. The adsorption data fit the Langmuir isotherm and its linearized form well, with thermodynamic data indicating the spontaneous and endothermic nature of the process. The FITEQL (V.4) and PHREEQC (V.2) computer programs are used to predict As(V) adsorption at various pH values (based on diffuse double layer models). The modeling results fit the experimental results very well and indicate that surface complexation modeling is useful in describing the complex AB surface during the adsorption process. This study shows that As(III) needs to be oxidized to As(V) for a favorable removal using AB and that AB can be a very efficient unconventional adsorbent for removing As(V) from water.

Increasing the arsenate adsorption capacity of neutralized red mud (Bauxsol).

The possibility of increasing the arsenate adsorption capacity of seawater-neutralized red mud (Bauxsol) through acid treatment, combined acid and heat treatment, and the addition of ferric sulfate (Fe(2)(SO(4))(3).7H(2)O) or aluminum sulfate (Al(2)(SO(4))(3). 18H(2)O) is investigated. The results show that acid treatment alone, as well as in combination with heat treatment increases the removal efficiency, with the combination providing the best removal. Adding ferric sulfate or aluminum sulfate, however, suppress the removal. The results also show that activated Bauxsol (AB) produced using combined acid and heat treatment can remove roughly 100% arsenate (at pH 4.5) with or without competing anions (i.e., phosphate, bicarbonate, and sulfate) when the initial arsenate concentration is < or = 2 mgl(-1). Furthermore, it is found that the adsorption process using AB is not accompanied by the release of unwanted contaminants, and TCLP results indicate that the spent AB is not hazardous. It is believed that the AB produced here has good potential as an alternative adsorbent to conventional methods for removing arsenate from water.

Social and institutional feasibility of recycling nutrients in waste in Southern Thailand.

The social and institutional feasibility of recycling plant nutrients in waste in three case study areas, Phattalung, Kuan Lang and Prik, in Southern Thailand has been studied. Three sanitation systems (existing with modifications and alternative) in each area have been evaluated with respect to their acceptance among the local stakeholders and accommodation within the Thai legal framework. Culturally, most proposed recycling methods were accepted by local users, and great interest was expressed towards many of the proposed sanitation systems, except recycling methods involving direct contact with human excreta in Prik (Islamic culture). The three existing systems were assessed to be the most convenient and practical among the nine, due to their low maintenance requirement and the low user fees. The proposed modified and alternative sanitation systems involved higher public participation and thereby a change in the understanding of where the responsibility of managing people's waste products should be placed. Institutionally all nine sanitation systems were accepted by local administrators and all recycling systems were well accommodated within the Thai legal framework. Thus recycling plant nutrients in waste seem both social and institutionally acceptable in Southern Thailand.

Technical, economic and environmental feasibility of recycling nutrients in waste in Southern Thailand.

Technical, economic and environmental criteria were used to evaluate the feasibility of recycling plant nutrients in kitchen waste, human excreta and sullage from households in Phattalung (urban), Kuan Lang (peri urban) and Prik (rural) in Southern Thailand. The difference in situation and context of the three areas called for individual solutions, and for each area three sanitation systems were evaluated. However, in all three areas recycling human excreta and kitchen waste via composting latrines was found to be more environmental feasible than human excreta managed in septic tanks or sub surface trickle irrigation and kitchen waste disposed of at landfill sites or treated at composting plants. Sullage should in Kuan Lang and Prik be used directly on garden crops, but in Phattalung be treated in waste stabilisation ponds before discharge, to be environmentally feasible. The economic feasibility results varied among the three areas and among the involved stakeholders: farmers and Kuan Lang administration benefited from recycling waste, at the expense of other private users, Phattalung municipality and Prik municipality. The main cause of these conflicting interests was lack of cost recovery and public participation, which should therefore serve as the fundament of any future environmental and economic feasible sanitation system.

Adsorption of arsenate from water using neutralized red mud.

The potential for using seawater-neutralized red mud (Bauxsol), a waste from aluminum manufacturing, as an adsorbent for removing As(V) (arsenate) from water is studied. Herein, adsorption characteristics are investigated and it is shown that adsorption follows the Langmuir model, with the adsorption constants indicating the feasibility of the process. Furthermore, the adsorption is found to increase with decreasing pH (i.e., ligand-like adsorption), higher adsorbent dosages, and lower initial arsenate concentrations. The effects of ions are also tested and it is shown that the adsorption of arsenate decreases in the presence of HCO3-, while Cl- has little effect, and Ca2+ increases the adsorption. Water quality assessment after treatment with Bauxsol indicates that none of the trace elements tested are released from the adsorbent. A TCLP leaching test also reveals that the used adsorbent is not toxic. It is foreseen that Bauxsol may be developed into an efficient low-cost adsorbent for (pre-) treating arsenate contaminated waters.

Availability and quality of solid waste and wastewater in Southern Thailand and its potential use as fertiliser.

Recycling nutrients to agriculture with waste in Southern Thailand has been assessed in three model-areas: Kuan Lang, Prik and Phattalung. Samples of biodegradable solid waste and gray wastewater were collected and characteris ed physically and chemically. At present nutrients in the biodegradable solid waste and wastewater are lost, but especially kitchen waste and grey household wastewater constitute a large fertiliser potential. The average daily per capita generation rate of household kitchen waste is 228 g wet matter, 0.65 g N, 0.16 g P 0.34 g K, 0.05 g S, 0.39 g Ca, 0.06 g Mg, 6.9 mg Zn, 0.29 mg Cu, 0.05 mg Ni, 0.02 mg Pb, 0.09 mg Cd and 0.006 mg Hg. The average daily per capita generation rate of grey household wastewater is 102 L, 2.4 g N, 2.4 g P, 4.2 g K, 2.0 g S, 2.2 g Ca, 0.82 g Mg, 42 mg Zn, 0.91 mg Cu, 1.6 mg Ni, 0.46 mg Pb, 0.20 mg Cd and < 0.06 mg Hg. The waste products generally contain higher amounts of K, Ca, Mg, Zn, Cu and Pb (relative to phosphorous) than conventional chemical fertiliser, while N, S, Ni, Hg and Cd is at the same level.