Wastewater treatment with vermi-filtration

By Rafael D. Guerrero III

Our world today has two major water crises – the lack of clean water for drinking and the pollution of water bodies (seas, rivers and lakes) with domestic, agricultural, and industrial wastewater. In Metro Manila alone, an estimated 2 million cubic meters of domestic wastewater is produced each day by its more than 20 million people. Only 17% of such volume is treated or processed into clean water; the rest ends up in Manila Bay and Laguna de Bay.

Domestic wastewater is of two kinds: the so-called “black water” consisting of human wastes from toilets and “grey water” from the kitchen and wash room. In the absence of a centralized sewerage system, most of the toilets in urban and rural areas are of the sanitary type (with septic tanks) or the open-latrine type. The collection and treatment of domestic wastewater in sewage treatment plants (STPs) prior to release of clean water into water bodies is an expensive process.

A sanitary, low-cost, environmentally-friendly, and efficient alternative for the treatment of domestic wastewater is through vermi-filtration – the aerobic biodegradation and biological filter of organic matter by bacteria and earthworms. Vermi-filtration was first done by the researchers of University of Chile led by Prof. Jose Toha in 1992.

A comparison of the conventional activated sludge process and vermi-filtration process of wastewater treatment.

In vermi-filtration, the domestic wastewater or raw sewage is spread on an open concrete vermi-filter bed with organic materials like sawdust, wood chips, coir, bark, peat and straw on the top layer and inorganic materials such as gravel, sand and mud at the lower layer. Composting earthworms as the “African night crawler” (Eudrilus eugeniae), “Indian blue” (Perionyx excavatus) and “red wriggler” (Eisenia fetida) are stocked in the vermi-filter beds at 10,000 (about 10 kilos) per square meter and “fed” with one cubic meter of sewage per day.

According to Dr. Rajiv Sinha, Senior Lecturer of Environmental Engineering, at the Griffith University in Brisbane, Australia, earthworms feed on the microorganisms (heterotrophic and autotrophic bacteria) that grow on the organic matter in the wastewater and produce vermicast (humus) that can be used as a soil amendment or organic fertilizer (high in nitrate and phosphate) for agriculture. The filtrate, on the other hand, can be used for watering plants.

In a study conducted at the University of Chile, the researchers reported that the treated water after vermi-filtration had 85% reduction of biological oxygen demand (BOD), 95% reduction of chemical oxygen demand (COD), 95% reduction of total suspended solids (TSS), and 99% reduction of fecal coliforms (FC) compared to the untreated water. The treated water was clear and odorless with an oxygen content of 3-4 parts per million.

Moreover, the researchers found that the cost of wastewater treatment with vermi-filtration was only US$0.05 per cubic meter compared to US$0.12 per cubic meter with the conventional activated sludge process. The vermi-filtration process also has a minimal energy requirement, lower labor cost, and much lesser emission of greenhouse gases (GHG) than the conventional process.

This appeared in Agriculture Monthly’s September 2018 issue. 

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