Treatment of seafood-processing wastewaters in mesophilic and thermophilic anaerobic filters
Wastewaters from fish-canning industries have a high concentration of organic polluting substances (10–50 g chemical oxygen demand L−1 [COD]) and, in some cases, a high content of sea salts (Cl−: 8–19 g L−1, Na+:
5–12 g L−1, SO2−
4: 0.6–2.7 g L−1). The presence of high sodium ion concentrations in wastewaters with high organic content traditionally is considered as a very negative factor for their anaerobic treatment. In fact,
both the presence of Na+ and SO2−
4, transformed into H2S during the anaerobic degradation process, may cause toxicity and inhibition on the methanogenic process.
This work deals with the operation and treatment efficiency of two lab-scale
mesophilic and thermophilic anaerobic filters (MAF and TAF, respectively). So that the adaptation of anaerobic sludge to high saline concentrations is attained, a prolonged start-up period of about nine months was necessary. After this, a stable operation and similar treatment efficiencies
were reached, even when organic loading rate (OLR) as high as 9 kg COD m−3 d−1 (TAF) or 24 kg COD m−3 d−1 (MAF) were applied at chloride concentration of 13 g L−1. At these conditions, the COD removal reached
73% (TAF) and 64% (MAF), and the COD methanized reached 69% (TAF) and 66% (MAF). The sulphate in the influent was removed practically completely, leading to a H2S concentration in the biogas between 3–4%.
In spite of the lower specific activity of sludge from MAF (0.21
g COD g−1 volatile suspended solids [VSS] d−1) than from TAF (0.66), the MAF reached a higher OLR than TAF. This fact can be explained because of the higher retention of sludge into MAF (72 g VSS L−1) than TAF (10 g VSS L−1).
Two practical conclusions may be derived from this work: the thermophilic operation needs the use of a packing material with a higher capacity to retain biomass and the mesophilic operation requires a more frequent detachment of biomass from the support in order to avoid clogging problems.
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Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year. Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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