Municipal solid waste pre-treatment: a comparison between two dewatering options

Abstract

In the field of Municipal Solid Waste (MSW) management, dewatering before combustion is adopted in particular cases. The aim is the modification of the waste characteristics in order to increase its LHV and allow an easier removal of glass, metals and other inert material. The process is named bio-drying when it is based on biological aerobic reactions; no auxiliary fuel is needed thanks to the exothermic reactions that develop under aerobic conditions. About 2.5 million t MSW /y will be bio-dried in 2006 when all the bio-drying plants under construction will be completed. When the process is based on an external supply of heat (generally obtained from auxiliary fuel), the option is named thermal drying. This is well developed for sewage sludge but less for MSW. In Italy we can find a few experiences of thermal drying on the oversieve from MSW automatic sorting. In this case the aim is the decrease of humidity for the production of Refuse Derived Fuel (RDF) as, according to the Italian regulation, the highest value of humidity for RDF is 25%. A few proposals of thermal drying have been proposed as a pre-treatment before combustion in two Italian towns where an incinerator has been planned. In both cases the proposal is integrated with the combustor (in order to use a part of the heat of the off-gases) and the aim is the preparation of the waste to an easier inert, glass and metals removal (for material recycling and for decreasing the impact of the incineration). The present paper shows a comparison between bio-drying and thermal drying taking into account MSW characteristics, environmental aspects, energy balances and costs. An additional comparison concerns the role of selective collection of biodegradable fraction in order to decrease the humidity of the residual MSW.

Drying methods for municipal solid waste quality improvement in the developed and developing countries: A review

“…Dryers use external heat sources or internal energy by organic waste decomposition [27,29]. The dryers have been used for environmental engineering applications such as RDF drying, sludge dewatering [27] and MSW drying for fuel and reduced disposal at landfills [24,33,34,45,46]. The most common drying methods recently used around the world for optimization of MSW quality are as follows:…”

“…Perazzini et al [23] suggest that the proper treatment of organic or inorganic solid wastes such as biodrying is necessary for economic and environmental interests to obtain added-value by-product through resource recovery, energy recovery and reuse. Therefore, the optimization of MSW quality by drying could offer the numerous benefits, including the easier recovery of recoverable materials [23,24], easier storage for the future, easier transportation and reduction of disposal costs [16,25,26], improvement of heating values of waste fuel [24,[27][28][29][30][31][32][33] for the efficiency improvement of thermal waste treatment process [6], less dependency on fossil fuels, reduction of waste odor by slowing down the deterioration of the waste [6,33], reduction of environmental impacts from open dumpsites and landfills [6, 12-14, 31, 34], and mitigation of global warming [6,35].…”

“…Most recent studies [6,16,23,24,27,31,[36][37][38][39][40][41][42][43][44][45][46][47][48] have majorly focused on biostabilization, biodrying methods, solar drying and thermal drying for the pretreatment of high organic concentration of solid wastes. Moreover, numerous studies [4, 22-24, 27-29, 31-34, 36-49] have also investigated the process, performance efficiency and economic feasibility of different drying methods for the quality improvement of solid wastes coming from industrial sector, municipal sector and agricultural sector.…”

Energy from municipal solid waste

“…It must be taken into account also that a complete bio-stabilization requires energy consumption and processing time longer than bio-drying. Indeed bio-drying can be performed in about two weeks while bio-stabilization needs even a few months [29].…”

Modelling the Potential Biogas Productivity Range from a MSW Landfill for Its Sustainable Exploitation

“…On the basis of the average composition of municipal waste and previous experimental studies [19], some considerations can be expressed: organic carbon is about 50% of organic matter (on dry basis) and the organic carbon potentially leading to biogas formation is about 50% of the total organic carbon. Pre-treatments of the organic waste also decrease the biogas potential: bio-drying and bio-stabilization perform a mineralization of the organic matter, whose carbon content is converted to CO2 by aerobic bacteria [20,21].…”