Dewatering Fundamentals

 

INTRODUCTION

Anaerobic treatment is a biological process that utilizes a mixed culture of bacteria in the absence of free oxygen to remove organic matter that is present in wastewater. The overall process yields a useful byproduct in the form of biogas, primarily methane (CH4) and carbon dioxide (CO2)). This unique feature means that much of the available energy in the wastewater is converted to a gaseous form, resulting in very little energy left over for new cell growth. In a nutshell, three significant benefits are associated with this process, namely the production of biogas energy, much less biosolids waste and low energy requirement for the treatment process, in addition to these benefits:

• less nutrients required;

• system can be shut down for extended periods without serious deterioration; and

can handle organic shock loads effectively.

As with any process, however, anaerobic treatment does have certain drawbacks, including the following:

• anaerobic treatment alone cannot achieve surface water discharge quality, i.e. post-treatment is required

• reduced sulfur compounds are produced, which need to be properly addressed in terms of corrosion, odor, and safety; and

• longer start-up period.

Several different anaerobic technologies are available in the marketplace. The best technology in one case may not be the best in another. Wastewater characteristics affect the success or failure of specific processes. Fixed-media processes seem to be most suitable for treating low-yield waste constituents, while suspended-growth reactors are most suitable for treating high-yield wastes that readily produce granules. However, with proper selection of organic loading rate and operating conditions, each system can treat almost any type of wastewater but possibly will not perform optimally. Unless previous experience is available with treating a specific wastewater, treatability tests are recommended highly.