Vol.:(0123456789) 1 3 Waste Biomass Valor DOI 10.1007/s12649-017-9907-z REVIEW A Review of the Use of Earthworms and Aquatic Worms for Reducing Sludge Produced: An Innovative Ecotechnology Mohammad M. Emamjomeh 1  · Mahsa Tahergorabi 2  · Mahdi Farzadkia 2  · Edris Bazrafshan 3   Received: 12 August 2016 / Accepted: 20 March 2017 © Springer Science+Business Media Dordrecht 2017 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 diferent types of municipal waste sludge. Sludge reduction by earthworms and aquatic worms are promising and relatively common technologies, espe- cially in small-scale communities in developing countries. Keywords Aquatic worm · Earthworm · Fertilizer · Sludge reduction Introduction The conventional activated sludge (CAS) process is the most widely used biological wastewater treatment process for both domestic and industrial waste [1, 2]. In going kilogram of organic pollution in activated sludge sewage treatment plants produces 250–400 g of untreated sludge. Components of sludge were classifed to be microor- ganisms, slowly biodegradable and non-biodegradable organic and inorganic material. The most better biologi- cal wastewater treatment process for treatment of munici- pal and industrial wastewater is an aerobic activated- sludge process [3]. In aerobic wastewater treatment large quantities of biodegradable waste sludge are produced [4]. The average sludge production is 0.4 kg VSS per kg COD [4]. Average of waste sludge is produced in world- wide 20–40 kg per population equivalent per year [4]. Waste sludge is made from wastewater treatment, a com- plex mixture of water, bacteria, and organic and inorganic materials, containing phosphorus, nitrogen compounds and various pollutants such as heavy metals and patho- gens [4]. In China, the production of dewatered sludge from wastewater treatment estimated for approximately Abstract 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 efect of environ- mental factors on sludge reduction by aquatic worms and earth worms, new perspectives, and the operational prob- lems involved. Sludge is an unavoidable, hazardous, and odorous substance formed in conventional water and waste- water 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 waste- water treatment plants. This denotes the necessity of a costly treatment process. A biological technology for pro- cessing 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 com- mon technology, especially in small-scale communities in developing countries. Studies showed that 20–40% of sludge is converted into worm biomass. The efectiveness of vermicomposting fertilizers in improving soil fertility * Mahdi Farzadkia mahdifarzadkia@gmail.com 1 Social Determinant of Health Research Center, Qazvin University of Medical Sciences, Qazvin, Iran 2 Department of Environmental Health Engineering School of Public Health, Iran University of Medical Sciences, Tehran, Iran 3 Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, Iran