Limitations Through TOC Correlations: A Five Facility International
Wastewater treatment plants (WWTPs) are challenged
with the objective of treating wastewater to a level that is acceptable for
discharge into receiving waters (lakes, streams, rivers, estuaries, bays, etc.).
Regulatory agencies require that WWTPs routinely measure and report by permit,
the biochemical oxygen demand (BOD) of raw and treated wastewater to determine
the strength and wastewater loadings to and from WWTPs (USEPA, 2000).
Although the BOD5 test is still a widely
accepted parameter by regulators for characterizing water and wastewater
quality, it is inaccurate, unreliable, not effective at low concentrations, and
it cannot be used for process control or real-time monitoring due to the time it
takes to receive test results, at least five days (Constable, 1979). Wastewater
treatment plants can discharge treated effluent that may not meet permit
limitations for up to five days before a compliance issue can be identified by
the BOD5 test.
TOC: A New Approach
The wastewater industry has expressed a need for an analytical test to replace
BOD5 that can provide quantifiable,
precise and timely measurements of receiving stream wastewater loadings and
plant removal efficiencies, in addition to providing monitoring and process
control capabilities. TOC and/or COD have been commonly accepted and used in
industrial wastewater treatment as key parameters for process monitoring and
control. Global regulations allow chemical oxygen demand (COD) or total organic
carbon (TOC) to be substituted for BOD5
when a long-term BOD5:COD or BOD5:TOC
correlation can be demonstrated.
Wastewater treatment professionals are very eager to make a change from the BOD5
regulatory reporting requirements. TOC as an alternative to the BOD5
analysis will save WWTPs in analytical costs and potentially could reduce
chemical and energy costs if used for process control purposes. TOC as a BOD5
alternative will also increase plant operations efficiency and response time to
waste loading upsets.
Although there have been many studies that examine the correlation of BOD5
to TOC; research is needed to demonstrate that TOC can be reasonably used to
monitor plant performance as an alternative to BOD5
measurements for permitting purposes. This research report presents the
correlation of BOD5:TOC for five
facilities of various flows, treatment levels and climates and present
site-specific equations for each site. The correlations and the statistical
significance of each are also summarized.
TOC Research Findings
A statistically significant BOD5:TOC
correlation was demonstrated when all BOD5
data sets throughout the treatment process including raw sewage, primary
effluent, and final effluent were plotted against their respective TOC data
sets. Using all BOD5 data sets throughout
the treatment process (from influent to effluent), is what is required to
demonstrate a site-specific BOD5:TOC
correlation to allow a TOC limit to be substituted for a BOD5
limit in permits.
When considering the final effluent data set independently (where low BOD5
concentrations are present), a statistically significant BOD5:TOC
correlation was difficult to be demonstrated due to the inherent inaccuracies of
and ineffectiveness the BOD5 measurement
at low BOD5 concentrations.
In addition, to guide wastewater treatment plants in developing a site-specific
TOC:BOD5 correlation that could be used
to allow a TOC limit to be substituted for a BOD5
limit in permits, an implementation protocol is presented.
Now Available for Immediate Download
Please see ITA's
newest research report regarding BOD5:TOC
correlations for more information.
Use ITA's report to learn how to correlate BOD5
to TOC for permit modification using the report's Implementation
Protocol for WWTPs to develop their own site-specific BOD5:TOC
This report also presents comparative analysis and
summary for 5 WWTPs of various flows, treatment levels and climates and
identifies long-term practices of using TOC as a process control
parameter-specifically to monitor the removal of organics in a
wastewater treatment process and the utilization of carbon balances.