Efficiency of Combined Co-composting, Vermicomposting, and Drying in the Treatment of Cadmium, Mercury, Helminths, and Coliforms in Sludge from Wastewater Facilities for Potential Agricultural Applications

Maria Aileen Leah G. Guzman1*, May Ann A. Udtojan1, Marylle F. Del Castillo1,
Emilyn Q. Espiritu1, Jude Anthony N. Estiva2, Jewel Racquel S. Unson1,
Joan Ruby E. Dumo1, and Jay Roy E. Espinas1

1Department of Environmental Science, Ateneo de Manila University,
Loyola Heights 1108 Quezon City, Philippines
2Aparri Engineering LLC, 131 Main St., Suite 180, Hackensack NJ 07601 USA

*Corresponding Author: This email address is being protected from spambots. You need JavaScript enabled to view it.


Sludge generated from wastewater treatment facilities has been applied in agriculture as soil conditioners. However, the incomplete and/or inappropriate treatment of wastewater may result in sludge that may still contain heavy metals, helminth ova, and coliforms posing a risk to both humans and the environment. This study assessed various pretreatment techniques such as co-composting, vermicomposting, and a combination of these on sludge samples to remove heavy metals (cadmium and mercury), helminth ova, and coliforms. Physico-chemical and biological analyses were used to compare untreated (i.e. raw) and treated sludge samples. The results showed that for the raw sludge, mercury (4.02 +/– 0.17 mg/kg) and cadmium (6.30 +/– 0.48 mg/kg) exceeded the limits specified under the Philippine National Standard (PNS) for Organic Soil Amendments of 2 mg/kg and 5 mg/kg, respectively. Laboratory examinations also revealed the presence of helminth ova (5 ova/g) and coliforms (10 CFU/g) in the samples. Sludge samples subjected to a combination of co-composting and vermicomposting resulted in the elimination of mercury and a significant reduction in cadmium concentration from 6.30 mg/kg to 1.12 mg/kg. No helminth ova were observed in the samples after further drying. However, both treated and untreated sludge samples had low nutrient content. The study highlights the need for raising public awareness and educating farmers on the potential risks associated with the use of raw sludge for agriculture.


The management of sludge produced from wastewater treatment facilities is one of the most expensive challenges faced by the wastewater industry that engineers and regulators are trying to solve (Metcalf and Eddy 2003; Sinha et al. 2009). The production of massive quantities of sludge has led to the development of various disposal methods including the use of landfills, incinerators, and land application. Among these, the use of sludge for land application is proposed to be the most resourceful and economical alternative method for disposal.  Sludge is a potential source of nutrients that can be used as a soil conditioner or fertilizer (Stadelmann et al. 2001; Metcalf and Eddy 2003). Several studies have shown that sludge contains compounds that provide a rich source of organic matter, nitrogen, phosphorus, potassium, and other plant nutrients that may be of agricultural value (EC 2001; Usman et al. 2012). The high organic matter in sludge can improve the physical characteristics of soils such as its structure, water retention, and porosity (Hossain et al. 2017). Hence, it is environmentally friendly and also an economically efficient method of solid waste disposal. . . . read more



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