Using Remote On-line Data Analytics to Identify Your Sewer Rats

Phil de Groot, TRILITY; Hugh Ratsey, The Wastewater Specialists; and Andre Dine, TRILITY

Over the Christmas and New Year holiday period 2020/21, the Rotorua Wastewater Treatment Plant (WWTP) was hit by at least three, separate, inhibitory discharges from unidentified sources. These caused significant loss of nitrification, with elevated ammonia concentrations in the treated effluent for several weeks. While this did not cause an immediate breach of concentration-based resource consent conditions, the annual consented total nitrogen (TN) load limits were exceeded.

Historically, trade waste monitoring in Rotorua has been limited to spot or 24-hour composite samples, typically on a monthly basis, with analysis at an accredited laboratory. However, given the severe incidents over the 2020/21 holiday period, which were not without precedence, the historical monitoring programme evidently did not provide an appropriate level of trade waste management.

Rotorua Lakes Council (RLC)’s wastewater system operations contractor, TRILITY, had a strong desire to identify potentially inhibitory discharges to the WWTP and improve WWTP performance and reliability. So, in a first for New Zealand, TRILITY engaged the Israeli company Kando, through their Auckland-based agent Detection Services, to supply and install on-line condition data analysis and sampling equipment at strategic locations in the Rotorua sewer network between November 2021 and February 2022. This included targeted data gathering from known trade waste dischargers, as well as at key pump stations and the WWTP inlet. Using artificial intelligence (AI), Kando’s software calculated a real-time “Pollution Index” (PI) at each monitoring location based on indicative parameters, and tracked out-of-spec discharges from source to WWTP.

While good performance of the Rotorua WWTP was maintained through the 2021/22 holiday period, the threemonth project identified significant out-of-spec discharges from two known trade waste discharges, plus suspected, significant, unknown discharges in other parts of the network. Samples of out-of-spec discharges were collected by automatic sampling, with the samplers triggered by Kando-identified Pollution Events (PE). Analysis of samples by conventional laboratory analysis and respiration-based toxicity testing (RBTT) confirmed the inhibitory nature of several discharges.

Through Co-Lab Water Services, which manages RLC’s trade waste compliance, rapid feedback was provided to key trade waste dischargers where PEs were identified. This allowed inadequate trade waste management practices to be quickly addressed, with one key trade waste discharger making significant improvements over a three-month period.

Following the three-month trial, TRILITY will be undertaking a full-scale, 12-month, Kando monitoring programme to hone in on areas of the network where unidentified PEs were detected during the initial survey period.