Collection systems with long residence will have anaerobic zones. Under highly negative redox conditions (no oxygen or nitrate/nitrite present), microorganisms that can utilize sulfate and organics as electron acceptors begin to grow on influent organics. We call these organisms sulfate reducing bacteria (SRB) and fermentative bacteria. The SRB are responsible for generation of sulfides and H2S, while the fermentative bacteria produce short chain volatile fatty acids. Both cause odors with the sulfide smelling of rotten eggs and the volatile fatty acids having sharp, rancid odors. I will list the most common control methods used in collection systems.
Redox potential or ORP is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. In wastewater biology, redox potential's importance concerns electron donors (often organic compounds measured as BOD5) and electron acceptors. This movement of electrons generates the energy used by the organisms. The redox potential in the water is directly related to the available electron acceptors. The most common wastewater electron acceptors are listed below:
I am a big proponent of using quick microscopic exams in wastewater treatment systems. The basic exam includes the following:
In the SV30 test, an high loading increases turbidity before anything else happens. Turbidity is due to free bacterial cells in the solution.
Multicellular indicator organisms - rotifers, nematodes, tardigrades - Are they a good or bad in wastewater treatment systems?
As a wastewater treatment system "matures" (decrease in soluble BOD5), dissolved oxygen concentrations eventually rise to levels that can support multicellular lifeforms. Unlike bacteria (prokaryotes) and protozoa (eukaryotes) which are all single cellular organisms, metazoa are more complex organisms with differentiated cells. These organisms feed on microbial floc and protozoa present. While seen with excellent water quality, an abundance of metazoa indicates an older sludge. The biggest problem with older sludges (very low F/M) is the increase in effluent turbidity and pin floc carryover in the secondary clarifiers. Common wastewater metazoa include:
The SV30 is possibly the easiest test done by wastewater treatment system operators. Fill a wide cylinder or settleometer with aeration basin MLSS and allow to settle for 30 minutes. This test is designed to give you settling rates for the MLSS and an estimate of how well secondary clarification will work. If all things are in good shape, just reading the 30 minute number is enough. However if you have problems with filamentous or non-filamentous bulking, secondary clarifiers have become undersized (either by hydraulic or solids carrying rate), denitrification, or have problems with pin-floc, fines, or turbidity - you should do more than just read the number after 30 minutes. Here is how to take advantage of settling tests using SV30 equipment.
Molecular testing includes qPCR or quantitative PCR which our lab at Aster Bio is developing into a powerful wastewater monitoring tool. After discovering organisms of interest using metagenomic testing or system surveys, custom test kits make qPCR a rapid, quantitive test for target microbial populations. What can be monitored with qPCR?
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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