Earthworms: nature’s chemical managers and detoxifying agents in the environment: an innovative study on treatment of toxic wastewaters from the petroleum industry by vermifiltration technology

Abstract

Earthworms are justifying the beliefs of Great Russian scientist Dr. Anatoly Igonin who said they are—“disinfecting, detoxifying, neutralizing, protective and productive”. Studies indicate that some species of earthworms can “bio-accumulate, biodegrade or bio-transform” any toxic chemicals including “heavy metals”, “organochlorine pesticide”, “herbicides”, and the lipophilic organic micro-pollutants like “polycyclic aromatic hydrocarbons” (PAHs). Worm vermicasts, due to the presence of “hydrophilic” groups in the “lignin contents” and “humus”, also provide wonderful sites for “adsorption” of heavy metals and chemical pollutants in wastewater. Vermifiltration of wastewater using waste-eater earthworms is a newly conceived novel technology with several economic and environmental advantages. The earthworm’s body and the their “vermicast” work as a “biofilter” removing BOD5 by over 90 %, COD by 60–80 %, TDSS by 90–95 %, and toxic chemicals and pathogens from wastewater. This was a pioneering work done on an extremely “toxic wastewater” from the petroleum industry. It contained mixture of “aliphatic” and “aromatic” volatile petroleum hydrocarbons (C 10–C 36) and “organochlorines” originating from the cooling liquids, waste engine and gear oil, waste transmission and brake fluid, grease, spilled petrol, and diesel oil. The aliphatic fraction contained cycloalkanes as well as a complex mixture of saturated toxic hydrocarbons. The aromatic fraction mainly consisted of PAHs, which are more toxic and persistent than the aliphatic part. The chemicals of concern were the total petroleum hydrocarbons (TPH), dichloromethane (DCM), dichloroethane (DCE), and t-butyl methyl ether (tBME). The tBME compound has raised global concern recently due to its high mobility and persistence in the environment and possible carcinogenicity. About 1,000 earthworms (species Eisenia fetida) were released in the soil of vermifilter bed. They not only tolerated and survived in the toxic petroleum environment but also bio-filtered and bio-remediated the dark-brown petroleum wastewater with a pungent smell into pale-yellow and odorless water indicating disappearance of all toxic hydrocarbons. The hydrocarbons C 10–C 14 were reduced by 99.9 %, the C 15–C 28 by 99.8 %, and the C 29–C 36 by 99.7 % by earthworms.