CHROMIUM TANNERY WASTEWATER EFFECTS ON
ALGAE OXIDATION POND AND PHYSICAL-CHEMICAL PROCESSES
Robert A. Ryder, Director
Pacific Environmental Laboratory
Kennedy Engineers Inc.
San Francisco, California 94105
INTRODUCTION
The development of rational pretreatment standards for industry that serve the requirements of the municipal waste discharger in achieving compliance with effluent and
recovery water quality requirements and at the same time can be relatively economically
achieved by industry are a challenge where cooperation and mutual understanding of
conditions and problems are quite necessary.
An on-site pilot plant investigation was conducted for a municipal sanitation district,
two tanneries, and the National Tanners Council to determine what levels of chromium
in the wastes could be effectively treated by algae oxidation pond, alum-lime coagulation and filtration-advanced waste treatment processes to meet stringent BOD, suspended
solids, nutrient, and chromium standards for discharge to a tidal estuary.   Tests were
conducted over a 15-month period at Napa, California, in pilot algae oxidation ponds
and in the laboratory to determine the effect of chromium in the range of 0.04 to
12 mg/l in wastewater in treatment performance.
It was found that concentrations of chromium as high as 0.5 mg/l could be treated
with no deliterious effects and an effluent containing 5 micrograms per liter of chromium in summer and 20 micrograms per liter in winter.
Corollary tests were conducted on the effect of pure chromium, chrone-tannery
waste, and organic chelated chromium on the growth of algae and daphnia in the pond
systems.   Certain algae acclimatized to high chromium concentrations and were effective
in its removal.
The seasonal changes in pH for higher values in summer in the ponds to lower values
in winter had the greatest effect on chromium removal.   Tests were conducted on the
possible resolubilization of chromium from pond sediments by lower winter pH conditions, but none was found.
The final outcome of the study was the determination of appropriate pretreatment
discharge requirements from the tanneries for a chromium concentration of 10 mg/l.
This provided, with dilution of municipal wastes,  a wastewater that may be effectively
treated and meet discharge requirements.   The pretreatment standard was, therefore,
set on a rational basis that reflects the cooperative approach by the tanneries and
sanitation district to meet effluent discharge standards in the most overall economic
manner.
BACKGROUND
The major industrial waste discharges to the Napa Sanitation District in Napa, California are from two tanneries that utilize chromium in the tanning of hides to produce
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