The valorization of wastewaters from the fish canning industry is of great concern, not only because of
the high quantities generated, but also economic and environmental benefits may result from a proper
treatment approach of the waste generated while reducing costs related to wastewater discharge.
A limiting factor for reuse and recycling treated fish canning wastewater into an industrial plant and
also for other uses is the high salt content, which persists even after conventional treatment. So, the
reuse of fish canning industrial wastewater was assessed by combining conventional treatments, such as
sedimentation, chemical coagulation-flocculation and aerobic biological degradation (activated sludge
process) followed by a polishing step by reverse osmosis (RO) and ultraviolet (UV) disinfection.
In this investigation all these processes were optimized in order to remove essentially the effluent
suspended particles (primary treatment), the organic matter content in the biological aerated reactor
(secondary treatment) and, finally, the remaining salts and microorganisms (tertiary treatment).
The overall removal efficiencies obtained were: 99.9% for dissolved organic carbon (DOC), 99.8% for oil
and grease (O&G), 98.4% for total suspended solids (TSS), above 96% for anions and cations and 100% for
heterotrophic bacteria expressed as colony-forming units (CFU). The final clarified effluent was found to
have the quality requirements to be recycled or reused in the industrial plant, allowing the reduction of
the effluent to be discharged, the water use and the costs of tap water for industrial use.
As regards the energy and chemicals costs, to obtain a treated effluent to be reused in the process costs
0.85 V/m3. This value can be reduced by about 60% if the goal is only to meet the legislated standards for
the effluent discharge into water bodies. Tap water for the industrial plant costs about 2.1 V/m3.
Usually, fish canning industrial wastewaters have a highly variable composition over time.
For a good performance of treatment processes it is necessary to limit that variation.
However, extended wastewater monitoring, including all relevant analytical parameters, is expensive.
This work proposes an efficient approach to minimize the analytical determina-tions number without compromising the global characterization goal. This way, fish canning industry wastewaters variability was assessed and interpreted through multivariate statistical tools application to analytical data obtained from a monitoring program carried out in a fish canning industry of northern Portugal. 23 physicochemical parameters were determined in 20 samples collected on an 8 months period. The results achieved by correlation analysis, principal component analysis (PCA) and cluster analysis (CA) led to the main water pollution sources identification and to the minimization of physical and chemical parameters number to be analyzed in order to achieve a correct wastewater characterization, at minimum cost. The main pollution sources proved to be the brine and eviscerating step waters.
Dissolved organic carbon (DOC), total suspended solids (TSS), conductivity, pH, Ca2+, F−and one of the parameters SO4 ,NO3 and PO4 were identified as important parameters that must be monitored in order to obtain an accurate characterization allowing to define themost appropriate wastewater treatment.
