Abstract
Background: Sewage treatment leads to the production of large amount of sludge, containing organic matter and nutrients and considering requirements for recycling could be used as fertilizer. The sludge may also contain various pollutants that pose serious harm to human health and the environment. This study aimed at characterizing the industrial sewage sludge and evaluating its capability as fertilizer with no or a minor pretreatment. Methods: The sludge’s organic matter and nutrient contents, heavy metals, organic and microbial contaminants were determined and compared to literature data and international guidelines. Results: The organic matter, nutrients, phosphorous, and exchangeable potassium contents of the sludge samples were significantly high as follows: 33.6 ± 2.85 %, 6.29 ± 0.16 %, 1.41± 0.01 % and 1.236 g/kg, respectively. The concentration of heavy metals was 94.3 ± 59.5 mg/kg. The concentration of heavy metals, organic contaminants, such as PCBs, BTEX, and PAHs, and microbial contents (coliforms & E. coli) were lower than those reported by other studies. Toluene concentration was high. Conclusions: All characteristics of the sludge samples, except for the toluene and microbial contaminations, were acceptable for its use as land fertilizer. Both toluene and microbial contaminants can be removed, using thermal conditioning as a pretreatment.
Highlights
Sewage treatment leads to the production of large amounts of sludge, and the treatment and disposal of sewage sludge are the most expensive steps [1,2,3,4]
The sludge may contain various pollutants with serious and harmful effects to human health and environment. Organic contaminants such as, PCBs, BTEX and Polynuclear Aromatic Hydrocarbons (PAHs), and pathogens are the main groups of sludge pollutants [5,6,7,8]
The influent wastewater was treated at a treatment plant in the following order: screening, cyclone grit removal, API grease and oil separator, equalization tank, anaerobic fixed bed reactor (AFBR), moving bed biological reactor (MBBR), settling tank and chlorination
Summary
Sewage treatment leads to the production of large amounts of sludge, and the treatment and disposal of sewage sludge are the most expensive steps [1,2,3,4]. Organic contaminants such as, PCBs, BTEX and PAHs, and pathogens are the main groups of sludge pollutants [5,6,7,8]. The quantities of these pollutants vary depending on the sewage source and the treatment processes. Sewage treatment leads to the production of large amount of sludge, containing organic matter and nutrients and considering requirements for recycling could be used as fertilizer. The concentration of heavy metals, organic contaminants, such as PCBs, BTEX, and PAHs, and microbial contents (coliforms & E. coli) were lower than those reported by other studies.
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