A Wessex Water wastewater treatment facility manages a combined influent wastewater flow from municipal and industrial clients. The combination and variation of municipal and high strength industrial wastewater flows makes it difficult to maximize aeration efficiency.
Annual energy use on site is in the region of £500,000. These costs are primarily comprised of aeration energy and UV disinfection. A target of a 10 - 20% energy savings provides a potential for £50,000 -100,000 in savings per annum with improved aeration efficiency.
The WWTP receives a combination of municipal and industrial wastewater streams. The treatment process combines two Activated Sludge (AS) treatment systems which receives 45% of flow and and a Brightwater Biological Activated Flooded Filter (BAFF), receiving 55% of total flow. All flows leaving the site pass through final UV treatment.
The SENTRY monitoring sensor is placed upstream of a Brightwater BAFF unit. The BAFF
consists of 5 treatment cells that contain small pea sized plastic beads for biomass growth / retention. The key advantage of these treatment units is that they also incorporate filtration so do not require settlement and / or settlement tanks. These treatment cells take themselves offline each day to go into a backwash to remove captured solids.
(1) Monitor incoming wastewater conditions and identify key biological imbalance
(2) Validate correlations between biological activity and organic loading to the facility.
(3) Develop historical data sets that show the weekly and daily biological activity trends
for influent wastewater.
(4) Use the generated microbial activity data sets to predict low organic loading time periods and reduce aeration costs for the BAFF.
1. Event Detection
During a 3-month period the SENTRY platform identified 21 imbalance events for biological activity. Greater than 70% of events were triggered by high precipitation and resultant inflow and infiltration.
2. Organic load correlation
The SENTRY platform is set to record a reading every minute with 1,440 readings in a 24-hour period. The MET readings are displayed on an online dashboard with a signal also sent to the on-site SCADA to integrate with other data being collected at the facility. Correlation to on-site manual BOD sample analysis and in-line COD analysis was carried out. The MET signal was demonstrated to track very well with the real-time COD analyzer while at the same time requiring only a fraction of the maintenance requirements.
3. Daily and weekly trending
A historical data set was generated for 3 months of data and statistically analyzed using a signal decomposition with key repeating trends identified. The weekly pattern of MET at this site shows a wider range compared to typical municipal sites, indicating the impact industrial discharge has on the facility. Highest loading to the system occurs late evening between 8 and 10 pm. MET shows a decreasing trend from midnight, with the lowest organic loading happening early afternoons between 12 and 3 pm.
The duration of lowest organic loading is larger on Sunday and Monday (10am-3pm), while onWednesday and Friday larger organic loads are observed. The lowest organic loading (and microbial activity taking place between 12 and 3pm is considered non-typical and indicated the role industrial discharge has on wastewater composition at the facility.
4. Organic load control and aeration optimization:
The historical trending from the SENTRY platform showed a consistent period of the day where we identified a lower MET reading. From the MET readings we identified the period from 12:00pm to 3:00pm as being the low-period of microbial activity. Overlay of this data with on-site dissolved oxygen readings from the AS plant clearly showed high dissolved oxygen readings that correlate to low periods of MET activity. These readings indicate periods of the day where the facility is being over aerated.
Based on these readings Wessex Water will divert more loading during the low organic loading periods from the BAFF reactor to the AS treatment system. This process optimization strategy allows for maximal aeration efficiency while allowing for a reduction in operating costs for the plant.
Based on the MET readings Wessex Water plans to divert more loading during the low organic loading periods from the BAFF reactor to the ASP. This flow re-direction will allow operators to minimize aeration requirements for the BAFF system (turning off blowers during low loading periods) and saving energy. The value of this strategy will result in a saving of £100,000 - 50,000 per annum with key savings in energy consumption as well as blower maintenace and cleaning.