Optimization and Control of Facultative Lagoon Systems Using ORP and Fermentation Analyses, 2001 Environmental Conference Proceedings

T. Norwood, J. Christiansen, M. Woehle, M. Kennedy--Many mill wastewater systems feature a combination of an aerated stabilization basin (ASB) and facultative lagoons. Literature describe ASB effluents with qualities of less than 100 mg/l BOD5 and less than 75 mg/l TSS, but NPDES discharge permits may require more stringent effluent quality. Facultative lagoons or hold-and-release ponds are often used to polish effluent to achieve less BOD5 and TSS, but facultative lagoons may offer limited efficiency due to solids buildup and anaerobic conditions, they also may become a source of fugitive odors.

A bleached board mill treats its wastewater in an ASB followed by facultative lagoons. Faced with a water quality permit that require an effluent of <20 mg/l="" bod5,="" the="" mill="" required="" optimum="" performance="" from="" the="" facultative="" portion="" of="" the="" treatment="" system.="" historical="" bod5="" removal="" rate="" was="" declining.="" while="" the="" options="" for="" capital="" improvement="" were="" investigated,="" mill="" personnel="" conducted="" an="" extensive="" investigation="" of="" the="" biochemistry="" in="" the="" main="" facultative="" lagoon.="" the="" investigation="" identified="" the="" presence="" of="" fermentation="" products="" in="" the="" lagoon="" effluent,="" which="" were="" indicators="" of="" poor="" bod5="" removal,="" anaerobic="" conditions,="" and="" oxygen="">

After characterization of organic acid products and total reduced sulfides, the mill conducted an experiment to convert the lagoon to an "anoxic" operation. An alternate election acceptor, sodium nitrate, was applied to decrease the population of sulfate reducing bacteria and select nitrate reducers, but literature described a large nitrate requirement to affect this change. To determine the minimal nitrate requirement and control nitrogen effluent residuals, two other measures were taken: Oxidation- Reduction Potential (ORP) monitoring was implemented as a control system, and a biochemical mixture with a non-specific nitrate reductase was applied to lower reaction energy potential. Subsequent monitoring of fermentation products, TSS, and BOD5 showed a marked improvement in lagoon effluent. The results showed an increase in net BOD5 removal (over historical rates) by controlling lagoon chemistry and preventing anaerobic conditions.

A reduction in the aqueous concentration of sulfides and mercaptans was also noted. This makes the techniques useful to many different ASB/facultative lagoon systems where potential odors are a concern.