Treatment of seafood-processing wastewaters in mesophilic and thermophilic anaerobic filters

Author： Mendez Ramon Lema Juan M. Soto Manuel

ISSN： 1061-4303

Source： Water Environment Research, Vol.67, Iss.1, 1995-01, pp. : 33-45

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Abstract

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.