LuminUltra – Waste Water
Identifying biological Excursions
Problem: A municipal wastewater treatment plant investigated a sudden increase in fecal coliform exceedance events
Facility: Conventional activated sludge plant with chlorine disinfection in southeastern Australia receiving municipal effluent
Size: 16.9 MLD
Investment: ATP was used to troubleshoot the problem over the course of one day with a total cost of <$1000
Economic Analysis: By fixing the problem quickly, a savings of $5000/month for additional chlorination was realised
Synopsis: In 2017, a municipal wastewater treatment plant experienced a sudden increase in fecal coliform exceedances. Plant staff had hypothesized that the issue was associated with excessive biomass in the bioreactor. To combat the exceedances the chlorine dose was doubled, and a plan was developed to increase waste rates from the bioreactor. Prior to additional wasting, a chlorination system audit was done using 2nd Generation ATP. The audit, which occurred over the course of one day, determined that the chlorination system achieved 95% removal of cATP. However, after the effluent leaves the chlorine contact chamber it travels down a 26 m channel on the backside of the bioreactor before reaching the effluent compliance point. The cATP was 200% higher at the compliance point relative to the chlorine chamber effluent. Armed with this information, the plant staff was able to quickly identify a leak between the bioreactor and the effluent channel. After fixing the leak the plant no long experienced fecal coliform exceedance.
Background: The disinfection system at a wastewater treatment plant in southeastern Australia was evaluated as a part of a plant wide audit using LuminUltra’s 2nd Generation ATP in September 2017. The plant provides secondary treatment and has a dry weather discharge of 16.9 MLD. The plant’s disinfection system consists of two parallel chlorine contact chambers.
The plant audit was initiated by high bacterial concentrations in the plant effluent. For several months, the plant experienced non-compliance events for fecal coliforms, with concentration reaching 2.5 times the compliance concentration of 100 CFU/100 mL. The plant staff had hypothesized that the problem was associated with the bioreactor, but could not identify the problem.
Testing Plan: During the disinfection system audit, samples were collected from four locations and tested using LuminUltra’s 2nd Generation ATP test kits. Samples were taken from the secondary clarifier outlet, the chlorine dosing point, the chlorine contact chamber outlet and the regulatory compliance point. The regulatory compliance point is at the end of an approximately 26 m channel leading to effluent discharge pumps and a water reuse system. The sample points are shown in Figure 1.
Results: The results from the disinfection system audit are shown in Figure 2. As expected, there was a considerable decrease (~88%) in cATP from the secondary clarifier to the chlorine dosing point. There was a further reduction in cATP observed through the chlorine chamber. However, between the chlorine chamber outlet and the compliance point the cATP increased (~200%). These two points are connected by an approximately 26 m long open channel on the downstream side of the bioreactor.
For disinfection system outlets, corrective actions are generally recommended when the cATP concentration is above 250 pg/mL. At the outlet of the chlorine chamber the cATP concentration was below the recommended value, but by the time the treated wastewater reached the compliance point the cATP was more than double the recommended value. ATP testing was able to quickly determine that the channel was the source of additional biomass, which was unexpected as there are no additional inputs and the channel residence time is relatively short, so significant regrowth was not expected.
Investigation: The results of the ATP testing prompted the plant staff to start to inspect the integrity of the shared wall between the bioreactor and the effluent channel. Their investigation revealed a broken seal (Figure 3) that was leaking mixed liquor from the bioreactor into the effluent channel. The broken seal was detected approximately two hours after the start of the ATP testing program and was able to be fixed shortly thereafter. The leak was small enough that it was not causing large amounts of mixed liquor to enter the treated wastewater channel, however this meant that the leak was very difficult to pinpoint. The lead operator determined that without ATP testing it would have been very unlikely that the leak would be been detected.
Additional testing 3 months after the leak was fixed confirmed that ATP concentrations at the chlorine contact chamber (165 pg/mL) and compliance point (134 pg/mL) were well below the recommended concentrations of 250 pg/mL.
Prior to ATP testing, the following actions were taken:
- Hypochlorite concentration was doubled to try and reduce fecal coliform non-compliance events (Cost = $5000/month1)
- Considerable time was spent developing a plan to waste solids from the bioreactor (Cost = $4000-50002)
ATP testing including test kit consumables and operator time was conducted for less than $1000. By solving the problem quickly with ATP, a monthly savings of $5000 was achieved.
1 Estimated based on a $70,000/year O&M cost sodium hypochlorite disinfection and dechlorination for an 11MLD
2 Estimated based on 80-100 hours @ $50/hour