Temporal Evolution of Linear Alkylbenzene Sulfonates and Heavy Metals in Sludge from Wastewater Treatment Plant

Abstract

Five homologues of linear alkylbenzene sulfonates (LAS)-LAS C-10, LAS C-11, LAS C-12, and LAS C-13 and total LAS-were monitored during a one-year period in primary, secondary, and digested sludge to evaluate their presence and temporal evolution. Extraction of LAS was carried out using microwaves energy, and determination was performed using high-performance liquid chromatographic- fluorescence (HPLC-FL). The results showed that concentrations of total LAS were between 9 337 mg/kg(-1) dry matter for primary sludge and 33.3 mg/kg(-1)(DM) for secondary sludge. Concentrations of total LAS were greater than 2 113 mg/kg(-1) in primary and digested sludge and were less than 260 mg/kg(-) in secondary sludge. On the other hand, the highest concentrations of LAS in primary sludge were found in summer, probably because of lack of rain during those months. Concentrations tend to be constant throughout the year in digested sludge. In addition heavy metals also were analyzed. Heavy metals, including zinc, copper, nickel, lead, and chromium are persistent environmental contaminants that cannot be destroyed. Biomagnification through the food-chain and potential accumulation in human tissues can cause both human health and environmental concerns. Concern regarding total heavy metal content of sludge limits sludge recycling for use on agricultural lands. This paper presents a comparative study of wastewater sludge that are going to be used as fertilizer based on the requirements of legislation proposed in the European Union. This research found that concentrations of total LAS in digested sludge are higher than the limits established in the proposed new draft.