Nutrient removal using spent coconut husks

Abstract

Wastewater management poses major environmental and economic problems in many small island developing states (SIDs), such as Trinidad and Tobago. Conventional wastewater treatment using activated carbon (AC) from charcoal is very costly. However, using spent coconut husks can be a cheap, environmentally friendly alternative source of AC for removing nitrogen and phosphorus in the secondary effluent. This study considered thermal and non-thermal, chemical activation methods to create four different AC treatments. The treatments considered included: virgin AC (thermally activated only) and subsequent acid treatments. Acid treatments were considered as an acidic environment, optimized nitrate and phosphate removal and reduced hydroxyl ion competition. Although all treatments effectively removed nitrates, virgin AC was ineffective in PO43-P removal when concentrations were less than 10 mg/L. This was probably due to naturally occurring PO43-P leaching from the coconut husk. The differences in removal efficiencies and adsorption capacities were not significantly different between treatments. Thermal activation was sufficient to remove NO3-N and PO43-P greater than 10 mg/L in experiments with batch stock solutions and the secondary effluent. Virgin AC can therefore be used as a potential substitute for conventional AC.