2. Methods
2.1. Preliminary characterization of screenings from different
wastewater treatment plants
As a first step towards the development of an adequate treatment
strategy for these wastes, quantitative and qualitative characteristics
of the production of screenings and sievings
(respectively collected from screens with gap sizes between 6
and 60 mm or below 3 mm) were determined from three municipal
wastewater 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 with
the recommendations of the European standard NF EN
14899:2005 (Characterization of waste – framework for the preparation
and application of a sampling plan), were done between
May 2007 and November 2008, each with a duration between 3
and 7 days.
The composition of the screenings sampled from each WWTP
and each campaign, determined according to the French standard
NF X30-466: 2004 (Characterization of municipal solid wastes –
analysis on dry product), was found to be relatively similar
Table 1
Characteristics of the wastewater treatment plants selected for the sampling campaigns.
The predominant materials in the screenings
were found to be sanitary textiles which accounted for
54.7–72.9% 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 of
3 mm or less) and the predominant fractions of the screenings
(screens with gap size from 6 to 60 mm) exhibited a high volatile
solid content which was found to be highly biodegradable as
shown by the biomethane potential.
Average biomethane potential (BMP) values (expressed under
normal conditions of pressure (1 atm) and temperature (0 C)) obtained
from screenings (from 191 to 271 Nml CH4/g VS) and from
sievings (from 289 to 377 Nml CH4/g VS) were found to be equal
or even superior to BMP values of wastes currently treated by
digestion at the industrial level. Indeed, Owens and Chynoweth
(1993) and Jokela et al. (2005) reported municipal solid waste
BMP values were between 180 and 220 Nml CH4/g VS and typical
methane production potential of sewage sludge is approximately
300–400 Nml CH4/g VS
Based on these observations, the present paper considers the
anaerobic digestion of screenings through the implementation of
a pilot-scale study. Parameters such as biogas production and composition
were used to evaluate the performance of the treatment.
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