MANTECH recently performed a demonstration of the PeCOD® COD Analyzer at two Water Treatment Plants (WTPs) in the mid-west United States. These plants have historically seen issues with taste and odor events related to Natural Organic Matter (NOM) fluctuation in their source waters, sometimes leading to spikes of disinfection-by product formation. The plants use the following in their process:
- Copper sulfate
- Coagulation with sodium aluminate
- Powder activated carbon
- Calcium hypochlorite
- Phosphate & Cl2
To safeguard the public interest by mitigating the possibility of similar events in the future, the plant management is investigating the implementation of peCOD on their source water intakes to monitor for NOM variation.
The peCOD parameter can be used to optimize coagulation processes for a WTP; knowing the oxidation state of the NOM incoming to a plant allows the operators to fine-tune the coagulation process to treat the exact right amount. An over-dosing of coagulant is not inherently an issue; however it leads to wasted coagulant and unnecessarily high operating costs, especially in the occurrence of a storm or other NOM-affecting event. An under-dosing of coagulant can allow a portion of the NOM make it through the treatment process and come into contact with the disinfection process, potentially forming carcinogenic disinfection by-products (DBPs) just before entering the distribution system. Keeping the right balance of coagulant dose/incoming NOM reduces operating cost while also minimizing the risk of DBP formation.
The demonstrations at the mid-west utilities validated the ability of the peCOD parameter to detect the incoming NOM to the plants, and the corresponding removal of NOM through each treatment process, shown in the graphs below:
The data showed a 78% reduction in peCOD measurement for Plant A from the raw water to final effluent, with a peCOD value of 3.1 mg/L in the water going to distribution. Comparatively, Plant B only showed a 57% reduction in peCOD measurement, with a final effluent value of 7.8 mg/L. Health Canada recommends a final treated COD value of <5 mg/L in it’s 2018 guidance document on NOM in Drinking Water Treatment. Read more about how peCOD can be used to mitigate the formation of DBPs in this case study.