MANTECH offers alternative COD monitoring for mill effluents
The EUREKA Cluster for Water (www.acqueau.eu) provides transnational collaboration for innovative projects in water and environment. Novel Concepts for the Reduction of Recalcitrant COD in Water Intensive Industries is a recent project that focused on the pulp and paper industry.
Recalcitrant COD can also be referred to as hard COD in some industries. It is composed of organics that do not readily oxidize under biological conditions and are problematic in pulp and paper effluents. MANTECH’s photo-electrochemical Chemical Oxygen Demand (peCOD) method was used to evaluate COD reduction by new technologies used at various stages of the pulp and paper wastewater treatment process.
The peCOD method eliminates the use of mercury, dichromate and concentrated acid and generates COD results in 15 minutes. The core of the peCOD technology utilizes the high oxidation potential of UV irradiated TiO2 nano-particulates to fully oxidize all present species. The testing range is 0.7mg/L-15000mg/L of COD. Incorporating dilution can extend this range.
The peCOD method is approved by the Ontario Ministry of the Environment and Climate Change (MOECC Method E3515). The peCOD-based method is also an approved ASTM International method (D8084-17) for surface waters and drinking water treatment plants (raw and treated water).
Through the pulp and paper project, MANTECH is working with a variety of international research partners to evaluate and verify the correlation of peCOD to conventional dichromate COD. FPInnovations, Pointe-Claire, QC, is one of the Canadian research partners working with MANTECH.
FPInnovations compared MANTECH’s marketready benchtop automated and prototype on-line peCOD analyzers to the conventional dichromate testing method using a variety of samples from both kraft and mechanical pulp mills across Canada. Both filtered and unfiltered samples were run in triplicate for COD by dichromate method while comparative filtered samples were run on each of the peCOD models.
The automated peCOD is a benchtop model for analyzing multiple grab samples. Sample preparation, such as filtering, is completed by the operator, with the remainder of the peCOD analysis running unattended. The prototype on-line peCOD is fully automated to analyze one sample stream at a time. It can filter and connect directly to a Supervisory Control and Data Acquisition (SCADA) system. Both systems were run at FPInnovations to verify their variability and robustness, using an abrasive sample matrix.
A recent article for PACWEST 2017  and a presentation at TAPPI PEERS 2017  concluded that solids in wastewater effluent do not significantly contribute to total COD. From a variety of primary and secondary treated effluent samples, including both kraft and mechanical pulp mill operations, COD from solids typically represented less than 2% of the total. This will not affect the over-all COD result obtained with the peCOD, as the technology requires sample filtering of at least 50 μm.
A strong correlation between the standard dichromate and peCOD method confirmed this with r2 values ranging from 0.92-0.99 on both peCOD models. On average, where differences existed, the peCOD method gave slightly higher COD results than dichromate. This could be because the peCOD more effectively oxidizes recalcitrant COD present in treated effluent samples.
Results obtained from FPInnovations were also confirmed by two research partners in Finland that are part of the Novel Concepts project.  The Finnish research partners were utilizing all peCOD models in two separate pulp and paper laboratories and one research laboratory. They were also using the prototype on-line peCOD, installed at the influent and effluent stages of a mechanical pulp and paper mill’s waste water treatment plant.
With the data currently being collected from all pulp and paper research partners, MANTECH is working on the next generation on-line peCOD analyzer that has the ability to operate remotely through a web-based platform.
Outside of the recalcitrant COD project, there is a full-scale pulp and paper facility using the peCOD to minimize cost and increase performance. A Chilean mill laboratory has installed three peCOD units; the system provides results to process engineers 2.5 hours faster than the dichromate method and, more important, within minutes of sampling.
This has led to a reduction in hypochlorite used for bleaching, no loss of product quality, lower organics in the waste water plant and reductions in the chemicals and energy used for treatment. The total saving over 12 months was $US3 million. The return on investment for the three peCOD units was only three days.
The strong correlation between peCOD and conventional dichromate suggests there is potential for peCOD as an on-line monitoring tool to help both in-mill operation and wastewater treatment optimization. The online model requires further development of the pre-treatment process to minimize operator maintenance. The bench-top peCOD is already being successfully used in mills and other industries. It is also a safer, faster and greener procedure to perform than conventional dichromate testing, protecting operators and the environment while positively influencing financial performance and sustainability.
MANTECH Inc., www.mantech-inc.com