A Review of the Use of Earthworms and Aquatic Worms for Reducing Sludge Produced: An Innovative Ecotechnology

The aim of the present work was to present a review of about 103 recently published studies into the use of earthworms and aquatic worms for reducing the sludge produced by wastewater treatment plants. Also, there will be a discussion of the use of sludge reduction by aquatic and earth worms, aspects that need attention, changes in the characteristics of these worms, the effect of environmental factors on sludge reduction by aquatic worms and earth worms, new perspectives, and the operational problems involved. Sludge is an unavoidable, hazardous, and odorous substance formed in conventional water and wastewater treatment plants. The previous research showed that the treatment and disposal of the excess sludge accounts for more than 40-60% of the total operational costs in wastewater treatment plants. This denotes the necessity of a costly treatment process. A biological technology for processing waste sludge is waste sludge reduction by worms (innovative technology). These worms are of two types: earthworms (vermicomposting) or aquatic worms. Sludge reduction by earthworms is a promising and relatively common technology, especially in small-scale communities in developing countries. Studies showed that 20-40% of sludge is converted into worm biomass. The effectiveness of vermicomposting fertilizers in improving soil fertility is 30-40% higher than that of chemical fertilizers. It is a low-cost technology system for the processing or treatment of organic waste. It is concluded the aquatic and the earth worms can reduce the different types of municipal waste sludge. Sludge reduction by earthworms and aquatic worms are promising and relatively common technologies, especially in small-scale communities in developing countries.