2. Methods2.1. Preliminary characterization of screenings from differentwastewater treatment plantsAs a first step towards the development of an adequate treatmentstrategy for these wastes, quantitative and qualitative characteristicsof the production of screenings and sievings(respectively collected from screens with gap sizes between 6and 60 mm or below 3 mm) were determined from three municipalwastewater treatment plants in the Region Rhône-Alpes(France), the main characteristics of which are shown in Table 1.A total of six sampling campaigns, conducted in accordance withthe recommendations of the European standard NF EN14899:2005 (Characterization of waste – framework for the preparationand application of a sampling plan), were done betweenMay 2007 and November 2008, each with a duration between 3and 7 days.The composition of the screenings sampled from each WWTPand each campaign, determined according to the French standardNF X30-466: 2004 (Characterization of municipal solid wastes –analysis on dry product), was found to be relatively similarTable 1Characteristics of the wastewater treatment plants selected for the sampling campaigns.The predominant materials in the screeningswere found to be sanitary textiles which accounted for54.7–72.9% of dry weight, along with the fine fraction (<20 mm)which accounted for 17.1–21.8% of dry weight (Table 2).Table 3 shows that the sievings (from screens with a gap size of3 mm or less) and the predominant fractions of the screenings(screens with gap size from 6 to 60 mm) exhibited a high volatilesolid content which was found to be highly biodegradable asshown by the biomethane potential.Average biomethane potential (BMP) values (expressed undernormal conditions of pressure (1 atm) and temperature (0 C)) obtainedfrom screenings (from 191 to 271 Nml CH4/g VS) and fromsievings (from 289 to 377 Nml CH4/g VS) were found to be equalor even superior to BMP values of wastes currently treated bydigestion at the industrial level. Indeed, Owens and Chynoweth(1993) and Jokela et al. (2005) reported municipal solid wasteBMP values were between 180 and 220 Nml CH4/g VS and typicalmethane production potential of sewage sludge is approximately300–400 Nml CH4/g VSBased on these observations, the present paper considers theanaerobic digestion of screenings through the implementation ofa pilot-scale study. Parameters such as biogas production and compositionwere used to evaluate the performance of the treatment.
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