COD of effluent water is high and we want to lower it. What can be done?
93 % of DOC is humic-like matter which is the natural end product of microbial activity. Further reduction cannot be made biologically. Activated carbon is not economical but precipitation of humics (pH or flocculants) may be a feasible strategy.
90 % of TOC (COD) is related to organic acids. After aerobic biologic treatment all acids were oxidised.
Also, other non-humic matter was oxidised and humics remain the only refractory matter after biologic treatment.
97 % TOC was destroyed. A further reduction of TOC with biologic methods is impossible.
MBR systems are gaining increasing recognition. The membrane selectively removes particulate biologic matter and dissolved biopolymers to some extent.
This makes the membranes also prone to fouling. The example shows a typical performance of an MBR system:
Biopolymers are removed by about 80 %.
Here, a municipal waste water was directly fed to a single stage RO-unit.
The permeate water had a TOC-value of only 10 ppb and – interestingly – fouling issues were negligible.
This water is very rich in starch from food production.
UF removed the starch quantitatively and selectively, all other lower molecular weight compounds break through.
Landfill leachates are sometimes treated with UF to reduce TOC further. #
In this example the leachate is very ”old” and microbially degraded and therefore consists mainly of humics which are not retained by UF.
LC-OCD can also be used to study extracts (prepared by DOC-LABOR) from UF or RO membranes.
Here, the alkaline extraction (pH 13) was far more efficient that the extraction at neutral pH. As to be expected, the extract consist exclusively of biopolymers.
Waste waters are sometimes re-used for technical purposes (reclaim) and membrane techniques are the state-of-the-art.
Here, the product water after RO had a TOC-value of only 50 ppb, but severely fouling of the RO membrane was observed.
The RO permeate showed biopolymers which sows that biofouling did not occur on the high-pressure side but the low-pressure side.