ANAEROBIC TREATMENT KEY TO POLLUTION CONTROL
AND SOLIDS DISPOSAL WITH ENERGY RECOVERY
FOR A FOOD PROCESSOR
Robert C. Landine, Senior Environmental Engineer
Albert A. Cocci, Environmental Engineer
T. Viraraghavan, Environmental Engineer
Graham J. Brown, Environmental Engineer
ADI Limited, Consulting Engineers
Fredericton, New Brunswick, Canada
A large potato processing plant was faced with the requirement of installing secondary
treatment. The company was also have difficulties in disposing of a large quantity of filter
cake, other potato waste solids and manure from its feedlot where cattle were being fed
screenings and some other potato wastes.
The authors' experience in anaerobic treatment opened the door to a novel approach to
the overall problem. Previous studies had already shown that a system employing anaerobic
treatment of process wastewater effluent after receiving only 10 mesh screening would be
best. In that case, major solid waste streams such as peel waste and wastes from by-product
processing lines were to be segregated for recovery in-plant and disposed separately. The
novel approach presented in this chapter entailed discharge of all solid waste streams into
the process sewer and subjecting the resulting wastewater to 10 mesh screening prior to
anaerobic treatment in a bulk volume fermenter (BVF). The key to the proposed solution
was the BVF, which is capable of treating a wastewater bearing a large concentration of
suspended solids (SS) and producing biogas while operating at 20-25°C. Compared to the
large quantity of primary filter cake and other solid wastes now produced, it was estimated
that only a small percentage of these solids, on a dry weight basis, will remain for disposal
after anaerobic digestion. It would become a stable sludge for disposal on agricultural land.
Waste aerobic biological sludge, removed in the final clarifier, will be returned to the BVF
for digestion and additional production of biogas.
The proposal entails continued trucking of screenings solids to the company's feedlot to
form part of the feed ration for the cattle. Due to the favorable balance between the animals'
intake and their manure output, the feed truck could carry manure supernatant (only) on
its return trip for treatment in the BVF system. This liquid manure stream will no longer
present a pollution threat to the nearby stream, but will enhance biogas generation and
receive a high degree of treatment prior to discharge into a large river. The biogas will be
recovered and supplied to the process boilers where it could displace approximately 20,000
liter/day of imported oil when operating under design loading conditions.
Although this approach resulted in a very large load (80,000 kg/day) of chemical oxygen
demand (COD), requiring secondary treatment, no difficulty was foreseen in meeting effluent
limits, and it was found to be the most cost-effective scheme.
Five or ten years ago, the approach would have been to segregate as much solids in a
"dry" state as possible inside the plant, followed by screening and good primary treatment,
complete with sludge dewatering. This approach would minimize the pollution load remaining for secondary treatment. Hence, the idea of discharging all the solids into the process
sewer for anaerobic treatment represented a radical departure from traditional waste treatment practice.
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