Treatment of seafood-processing wastewaters in mesophilic and thermophilic anaerobic filters
Authors: Mendez, Ramon; Lema, Juan M.; Soto, Manuel
Source: Water Environment Research, Volume 67, Number 1, January/February 1995, pp. 33-45(13)
Publisher: Water Environment Federation
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.