Some of my colleagues have a class in water quality that is being taught in our department, and the question arose because of some municipal wastewater treatment plant samples that are from the Houston area that were given to students to examine for TOC and other parameters. They asked me about it, but I don't know near as much about what municipal and industrial treatment plant streams register on TOC as I do about natural waters.
I'm just curious what others see out there for TOC and DOC at different points within the processes and with different kinds of treatment facilities, both industrial and municipal. Are there typical values? Is there high variability? How much reduction in TOC can generally be received and/or is regulated for the effluents? Is the identity of the compounds in TOC or DOC significant? Does anyone ever have a regulatory burden that is more directed at TOC or DOC in particular? These are all broad questions I know. I'm just hoping to get some more general information. Oh and if you give me some info on DOC, please specify if you used the most typical 0.45 micron filtration size, or if you prefer and/or are required to have a different filtration size.
This is the 'ne plus ultra' of water-quality sampling methods.
http://water.usgs.gov/owq/FieldManual/
The TOC and DOC content of wastewater influent and effluent is highly dependent on source, region, seasonal variations, weather conditions and operational conditions of the plant. Hence, a high variability can be expected. Most of the values I know from effluent vary between 1 and 20 mg L-1 DOC, with most of the values in the range of 8 mg L-1. If the secondary settler works properly, the TOC will be in the same range. Influent, has very broad ranges and off course, due to the presence of suspended material, TOC and DOC differ significantly. I expect influent DOC values to be in the range of 10-few hundreds mg L-1 carbon.
DOC is generally defined as the carbon that is left after 0.45 um filtration. This is the standard method (APHA).
Mostly, if wastewater is considered (rather than drinking water), COD is a more frequently used parameter, of which limits are defined. E.g. in Belgium, the COD limit of effluent is 125 mg O2/L.
Organic matter in municpal wastewater consists of insoluble matter, natural organic matter originating from drinking water, soluble microbial products (biomolecules produced by the activated sludge) and recalcitrant organics such as micropollutants.
Wim and Stephen, thank you for these helpful answers. I have read several state level guides on water quality sampling, but I have not reviewed the USGS level guide. I will certainly review it now for good background for both reserach and teaching.
And I do appreciate having some typical values that Wim has seen in Belgian WWTP facilities for TOC and DOC. It makes intuitive sense to me that many regulartory limits for WWTPs might be COD rather than TOC or DOC since in the end they are concerned often most with oxygen depletion rather than increasing the amount or types of carbon in the surface water. I am someone who studies micropollutants in the receiving surface water as you mentioned in your response, and to me it does matter how much TOC and DOC is in the effluent. I'm not usually not too worried about the COD part of it. It seems like this is is one of those instances where the regulations drive what is commonly measured, and it is good for the facility. However, for other types of pollutant effects like micropollutant partitioning to sediment and biota, the OC is more important to know. Oh well.
Nathan, an interesting comment you made on that. As you probably know, regulation with respect tot micropollutants is in full development worldwide. E.g. in Europe, we have the "European water framework directive", which is a regulatory guideline that has to be translated to national regulations in all European countries. This is almost completed now. This directive includes a list of 33 priority comounds that will be restricted in future. (in contrast to the U.S., where (i think) regulations are merely developed at state level, most of environmental regulations in European countries were derived from directives from the European Parliament and Council). Some of the listed compounds are micropollutants.
This will have a severe impact on wastewater treatment in Europe! The WWTPs will have to meet the future effluent requirements with respect to micropollutants and hence, tertiary treatment (e.g. with ozone) will be needed. These tertiary treatment technologies are very important in my research and one of the most relevant parameters to understand and control those processes is.... DOC! So I guess, like you stated ("measurements driven by regulation"), DOC will be of main importance in the near future WWTP context.
What is the new version apparatus applied in organic geochemistry analysis.
I just read your comments here with regards to DOC and I was wondering if you have any good references that can be used for such a statement in a paper?
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