Wastewater Treatment Systems

Biological treatment - the use of bacteria and other microorganisms to remove contaminants by assimilating them - has long been a mainstay of wastewater treatment in the chemical process industries (CPI). Because they are effective and widely used, many bio logical-treatment options are available today. They are, however, not all created equal, and the decision to install a biological-treatment system requires ample thought. When considering biological wastewater treatment for a particular application, it is important to understand the sources of the wastewater generated, typical wastewater composition, discharge requirements, events and practices within a facility that can affect the quantity and quality of the wastewater, and pretreatment ramifications.

Consideration of these factors will allow you to maximize the benefits your plant gains from effective biological treatment. Those benefits can include:

* Low capital and operating costs compared to those of chemical-oxidation processes
* True destruction of organics, versus mere phase separation, such as with air stripping or carbon adsorption
* Oxidation of a wide variety of organic compounds
* Removal of reduced inorganic com pounds, such as sulfides and ammonia, and total nitrogen removal possible through denitrification
* Operational flexibility to handle a wide range of flows and wastewater characteristics
* Reduction of aquatic toxicity

The use of microorganisms to remove contaminants from wastewater is effective and widespread. To choose the right system from the many options offered, understand the various techniques available and evaluate them based on your requirements.

SELECTION CRITERIA

Biological-treatment technologies vary greatly in their strengths and weaknesses. The following are application criteria, which are normally relevant in evaluating various biological treatment options for the CPI:

• Bioassay/toxicity control - The ability to control and minimize the impact of toxic constituents in wastewater on indicating organisms when the treated water is released

• BOD removal efficiency - The ability to remove biodegradable, organic com pounds

• COD removal efficiency - The ability to remove chemically oxidizable substances that may or may not be biodegradable

• O&M costs - The cost to operate and maintain the treatment method

• Sludge production - The amount of residual biological solids generated by the bio logical-treatment process

• Sludge disposal costs - The cost to collect, dewater and dispose of residual sludge from the treatment method, either on-site or off-site

• Performance in winter and summer - The degree in which high or low ambient temperatures will affect biological treatment

• Performance on high- and low-temperature water - The degree in which high and low wastewater temperature will affect biological treatment

• Operator attention - The relative amount of time required to operate the biological treatment system

• Upset recovery - The amount of time it takes for a treatment method to recover from upset conditions. Upset conditions are defined as abnormal variations in the flow or characteristics of the wastewater, which can detrimentally affect a biological treatment system

• Expandability - The ease of expanding the treatment capacity to accommodate either an overall plant expansion or an increase in loading

• Nitrification Efficiency - The relative ease of converting ammonia contained in wastewater to nitrates

• VOC containment - The relative ease with which the biological treatment equipment can be enclosed to contain and collect VOC emissions

• VOC stripping potential - The relative ease with which the biological-treatment system will strip volatile organic compounds from the wastewater

• Ease of installation - The total amount of time and labor required to install the treatment method

• Energy efficiency - The amount of energy used by a treatment method

• Ease of secondary containment - The ability and ease with which the treatment system can be provided with secondary containment in case of overflow, spills or leaks

• Space requirements - The area required by the treatment method

The use of microorganisms to remove contaminants from wastewater is effective and widespread. To choose the right system from the many options offered, understand the various techniques available and evaluate them based on your requirements.