68    ANAEROBIC PILOT PLANT STUDIES FOR DAIRY PLANT
WASTEWATERS
Enos L. Stover, Principal Engineer
Reinaldo Gonzalez, Project Engineer
Stover & Associates
Stillwater, Oklahoma 74076
INTRODUCTION
Biological treatment of high strength industrial wastewaters by aerobic treatment methods has
often been limited by the variable nature of the wastewater, economics of treatment, excessive sludge
production, and physical limitations relative to adequate oxygen transfer and solids settling and
thickening problems. On the other hand, anaerobic treatment of high strength wastewaters can be
highly feasible while not being limited by these problems. With many types of wastes, high treatment
efficiencies can be achieved by anaerobic treatment along with low sludge production and production
of enough methane to make the treatment facilities self-sufficient from an energy standpoint.
The key to maintaining process control and stable operations in biological treatment systems
(aerobic or anaerobic) is to provide proper environmental conditions to the biomass or bacteria in the
system. Imperative for successful design and operation of anaerobic systems is matching of the
number of microorganisms in the system to the organic substrate loading rate to the system, or
controlling the food/microorganism (F/M) ratio. Accurate prediction and modeling of both treatment performance and methane production has been accomplished when substrate utilization and
methane production were expressed as functions of the mass substrate loading rate (F/M) by mono-
molecular kinetics for both suspended growth and fixed-film systems. Extensive evaluation of anaerobic reactors by the authors over the past few years has shown that these systems can be designed and
operated on a reliable basis. The authors have developed accurate biological kinetic analysis procedures for anaerobic systems that allows comparisons of wastewater treatability characteristics whether
in full-scale or pilot treatment systems. This approach has been successfully used to compare full-scale
operations with pilot study data. Test results, operating data, and experience gained with suspended
growth anaerobic systems treating dairy processing wastes (whey and washwater) from cheese production are presented herein.
INVESTIGATIVE PROGRAM
The primary factors that were envisioned at the beginning of this study to influence both the
biological treatment kinetics and the sludge flocculation and settling characteristics follow:
• Hydraulic loading to ensure adequate retention time is present in the anaerobic reactor
for sufficient degradation of organic materials.
• Organic loading to the unit for optimization of biological growth rate.
• Appropriate pH conditions for the growth of acid and methane forming bacteria.
• Volatile acid to alkalinity ratio.
• Sufficient macronutrients such as nitrogen and phosphorus.
• Trace quantities of micronutrients such as molybdenum, nickel, cobalt, copper, manganese, potassium, and others.
• Absence of toxic materials such as heavy metals which may inhibit bacterial growth.
• Adequate hydrolysis of the wastewater (not necessarily through a separate hydrolysis
step, but rather through appropriate environmental and loading conditions).
As a result of the diversity of the nature of environmental factors that could possibly be creating an
influence on the successful operation of a full-scale anaerobic system, the decision was made to
operate a number of pilot bench-scale anaerobic reactors under controlled environmental conditions
in order to determine problem areas and define proper environmental conditions for successful,
reliable operations.
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