74    THE ANAEROBIC TREATMENT OF TANNERY
WASTEWATER
Huang Yong, Lecturer
Department of Environmental Protection
Suzhou Institute of Urban Construction and Environmental Protection
Suzhou, Peoples Republic of China
INTRODUCTION
In the last twenty years some new processes and devices have been developed for anaerobic treatment, such as the anaerobic filter,1 the up-flow anaerobic sludge blanket reactor,2 the anaerobic
expanded or fluidized bed reactor,3'4 etc. With the efficiency and effect improved, the development of
these new devices suggests that the anaerobic process is expected to become a valuable method in
wastewater treatment. Several kinds of industrial wastewater have been successfully treated by means
of anaerobic processes in laboratory research, pilot-scale studies, and full-scale operations. Because
anaerobic treatment has the advantages of high organic load, low energy consumption, small amount
of sludge produced and simple equipment, and can recover methane gas as useful energy, it is widely
investigated and generally recognized to have great potential as an economical and effective approach
to wastewater treatment.
In order to make a more widely practical use of anaerobic processes, there are problems to be
resolved in two aspects. They are, first, further development and perfection of the theories, structures, design approaches and measures in management of the available treatment systems, and applying these in practice; and second, expanding the range of wastewater which is permitted to be treated
by the anaerobic process. So far, more studies are carried out in the treatment of food processing
effluents and have thus gained some success in practical operation. But for other industrial effluents
the research has not been much and not enough in depth. The practical application was rarely seen.
Tannery wastewater, containing a high concentration of organic substances, including proteins, fats
and vegetable tanning materials, which should be degraded by anaerobic microorganisms, is an
important industrial pollution source of some bodies of water. The purpose of our research is: 1) to
investigate the feasibility of anaerobic treatment of tannery wastewater; 2) to determine its characteristics; and 3) to seek a new way for treatment of tannery wastewater.
EXPERIMENTAL PROCEDURE
Our experiment consisted of two pieces of apparatus. Reactor I, having an effective volume of 20
liters, was intermittently fed with wastewater 2 to 4 times per day. Reactor II, having an effective
volume of 3.7 liters, was operated in a continuous flow manner. Both reactors were stirred frequently
so that the influent was well mixed with the contents of the reactors. The experimental systems are
shown in Figures 1 and 2. Wastewater used in the research was effluent from a tannery factory, a
mixture of effluents from those working procedures of skin-washing, degreasing, softing and vegetable tanning, in addition to small amounts of sodium sulfide-containing wastewater. Anaerobic sludge
was taken from a digestion tank of a municipal sewage treatment plant. During the start-up period of
two months, by means of adding the tannery wastewater into domestic sewage with gradually increasing proportions of wastewater, the seed sludge was adapted to the complex compositions of tannery
wastewater and seemed to increase the ability for decomposition of the organic matter in the wastewater and resulted in the production of biogas. Operation was maintained at a temperature of about
35°C during the start-up period and at about 31.5°C during most of the time of the experimental
operational period. Influent pH was adjusted to near neutral by adding HC1. Experimental operations
lasted five months from April to August, 1984.
EXPERIMENTAL RESULTS
The influence of hydraulic retention time (HRT) and influent concentration of COD on the efficiency of treatment is shown in Figures 3 and 4, respectively. The results of the experiments showed
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