OC San P1 and P2 Operating Range Values (ORVs) and plant performance during sampling period.

AS = activated sludge, TF = Trickling Filter, SC = Solids Contactor, MCRT = mean cell residence time, BOD-T = total biological oxygen demand. MCRT for all secondary treatment processes are calculated daily by OC San using the below equations. OCWD proposes to use the OC San-calculated values of MCRT for assessment of ORVs related to LRV credit value. BOD-T (P1 TF) is measured by OC San as a daily composite. Mean Cell Residence Time (MCRT) Calculations: P1 Activated Sludge Processes MCRT = (Volume of reactor x MLSS) ÷ [(WAS flow x WAS MLSS) + (Effluent Flow x Effluent TSS)]; where MLSS = mixed liquor suspended solids, WAS = waste activated sludge, and TSS = total suspended solids. P2 Trickling Filter Solids Contactor MCRT = [(Volume of reactor x MLVSS) + (Volume of reactor RSS VSS)] ÷ [(Waste Flow x RSS VSS) + (Effluent Flow x Effluent VSS)]; where MLVSS = mixed liquor volatile suspended solids, RSS VSS = raw sewage sludge volatile suspended solids, and VSS = volatile suspended solids. (XLSX)</p

Statistical attributes of the log removal values calculated for each microbial target using the covariance-based approach and the modified Monte Carlo approach.

Statistical attributes of the log removal values calculated for each microbial target using the covariance-based approach and the modified Monte Carlo approach.</p

Summary of the log removal values (LRVs) generated by the covariance analysis approach for cultivable enteric viruses, enterovirus (ddPCR) and norovirus GII (ddPCR), MS coliphage, and SOM coliphage.

Summary of the log removal values (LRVs) generated by the covariance analysis approach for cultivable enteric viruses, enterovirus (ddPCR) and norovirus GII (ddPCR), MS coliphage, and SOM coliphage.</p

Summary of percent recoveries for all virus targets.

Average recovery percentages shown in bold were used to correct each respective native dataset, e.g., 120% recovery was used to correct all native P1 raw influent samples for SOM coliphage. The average percent recovery used to correct the native cultivable enteric virus dataset was obtained by taking an average of SOM, MS and Poliovirus recoveries, which are shown as the bold mean values for Poliovirus. An average recovery value was not used to correct the native molecular (enterovirus and norovirus GII) datasets. (XLSX)</p

Fig 2 -

Probability distributions for cultivable enteric virus concentrations obtained from raw influent and secondary effluent samples taken at OC San P1 (left) and P2 (right). Each point represents one sampling event and the solid line represents a best-fit regression. The coefficient of determination (R2 value) is also shown. Raw influent and secondary effluent cultivable enteric virus data obtained from both P1 and P2 are lognormally distributed.</p

OC San sampling location description.

A total of six (6) sampling locations from OC San P1 and P2 were monitored. Sampling locations for OC San P1 were raw wastewater influent, trickling filter (TF) secondary effluent, activated sludge 1 (AS1) secondary effluent, and activated sludge 2 (AS2) secondary effluent, while sampling locations from OC San P2 consisted of raw wastewater influent and trickling filter/solids contactor (TF/SC) secondary effluent. Sampling at P2 was limited to characterizing the TF/SC process and not other parallel treatment processes. Raw wastewater entering OC San P1 is treated through preliminary screening and primary clarification with chemical addition and is then diverted into one of two secondary treatment trains that operate in parallel (trickling filter process or activated sludge process). Raw wastewater from P1 was collected after primary bar-screening but before primary clarification and chemical addition. Secondary effluents generated by three parallel treatment processes at P1 were sampled in this study. The first P1 treatment train routes the primary effluent through a trickling filter (TF) process followed by secondary clarification. Treated effluent from the TF process was sampled. P1 primary effluent is also sent through two parallel trains of the activated sludge (AS) treatment trains, designated separately as AS1 and AS2. Secondary effluent samples taken from each AS process following secondary clarification was sampled. Both AS trains operate in the nitrification-partial denitrification (NDN) mode. The major difference between the AS1 and AS2 processes is that AS1 does not receive mixed liquor return, while the newer AS2 facility does receive it. Microbial concentrations of both the AS1 and AS2 effluent streams from P1 were of interest due to the operational differences between the two processes described above. (DOCX)</p

Performance monitoring and ORV results.

Performance data from OC San P1 and P2 were collected to determine a recommended operating range value (ORV) for each OC San treatment process. Total biological oxygen demand (BOD-T) was selected as the ORV for the OC San P1 TF process. An upper baseline threshold for BOD-T is proposed because higher-than-normal BOD-T (30-day running average of > 26 mg/L) in this sampling location would suggest deviations from the typical performance that was documented during the enteric virus sampling. Lower baseline thresholds of Mean cell residence time (MCRT) was selected and proposed as the ORV for OC San P1 AS1, P1 AS2, and P2 TF/SC treatment processes. Lower thresholds were chosen because a lower-than-normal MCRT (Giardia and Cryptosporidium removal credit. In addition to this, OC San effluent must meet a specified turbidity requirement to provide blended secondary effluent to the AWPF. Using the described ORVs framework for the overall potable reuse project, each of the four OC San effluents serving GWRS features an ORV, as well as the combined (blended) effluents in the form of MFF and MFE, must meet their respective ORVs to receive virus LRV credit. (DOCX)</p

Concentrations of enterovirus and norovirus GII (ddPCR).

Gene copy detections of enterovirus (top row) and norovirus GII (bottom row) using droplet digital Polymerase Chain-Reaction (ddPCR) for raw and secondary wastewater from OC San Plant No. 1 (left panels) and OC San Plant No. 2 (right panels). The gap in sampling corresponds to a study interruption due to the SARS-CoV-2 pandemic. (TIF)</p