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Fluorescence-Based Optimisation Of Sewage Treatment

Final Report Summary - FLUORO-BOOST (Fluorescence-Based Optimisation Of Sewage Treatment)

Aim of the project
Our primary aim was to quantify the relationship between the fluorescence of sewage and more traditional analytical techniques at laboratory and full scales. These relationships were used to provide a novel, rapid and robust means of assessing wastewater treatment works (WwTW) performance, which could further help to optimize activated sludge process (ASP) performance and energy input. Meeting this aim overcomes the well-documented limitations of the BOD test and provides the water industry with a simple robust technique to ensure compliance with quality objectives whilst minimizing energy usage; thus delivering tangible environmental and financial benefits.

Summary of work towards objectives
Specific objective 1 (SO1) addressed by Task 1: To quantify the relationship(s) between fluorescence of wastewater samples and their chemical and microbiological quality through laboratory experiments of discrete samples of crude, settled and activated sludge process (ASP) – treated wastewater and final effluent taken from wastewater treatment works (WwTWs) and also discrete samples of synthetic wastewater.
Samples were collected from 5 WwTWs serving different areas in the West Midlands, UK: Kidderminster, Worcester, Spernal, Finham and Minworth. Wastewater was sampled at three different times of the day (9 AM, 12 PM and 3 PM) to ensure variability of the organic matter present in the sample. Analyses were made for fluorescence (using 2 steady state spectrofluorimeters and 2 portable fluorimeters), absorbance, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC) and pH.
Specific objective 2 (SO2) addressed by Task 2: To apply (and, if necessary, refine) the relationships identified in SO1 in a laboratory scale ASP and to examine the effect and impact of real-time changes in wastewater quality.
In order to achieve SO2, Dr. Carstea has led the design and manufacturing of a new laboratory scale ASP for the continuous flow trials. In order to ensure variability in the character and quality of wastewater, which was used as feed for the laboratory scale ASP, samples were taken from the 5 selected WwTWs. The experiment was divided into four continuous flow trials: the first three lasted for three weeks each and the forth trial for seven weeks, to evaluate the process at longer time scales. Fluorescence probes and 1 portable fluorimeter were placed into the effluent collection tank for real-time measurements. Discrete samples were collected from the effluent and feed tanks for measurements of fluorescence (with the steady state spectrofluorometers), absorbance, BOD, COD, TOC, mixed liquor suspended solids, volatile suspended solids, turbidity, ammonia, nitrates and total phosphates.
Specific objective 3 (SO3) addressed by Task 3: To apply the relationships at full scale WwTWs in order to demonstrate the effectiveness of fluorescence intensity as a novel and innovative process control and wastewater characterization technique, which can be utilized effectively for the real-time monitoring and control of WwTW operation.
In order to undertake the real-time fluorescence monitoring experiment, Finham WwTW was selected. Four portable devices were installed at the final effluent point. Two submersible probes measured peak T (microbial fraction), peak C (humic fraction), pH and conductivity. The other two devices measured ex-situ, using a flow through system, peaks T and C. The devices were chosen in order to check the feasibility of implementing submersible and cuvette-based instruments. The instruments were set up to record at intervals between 5 – 30 min. Grab samples were collected twice each week and measured in the laboratory with benchtop spectrofluorometers. In addition, the grab samples were analysed for absorbance, BOD, COD, TOC, ammonia, phosphate and nitrate. The experiment was run continuously for a month to assess the variability of the effluent quality.

Main results
• A large database was built with measurements of fluorescence and standard parameters for samples collected during all tasks to obtain a strong relationship between parameters. The outcomes of this analysis challenge the current views on the relation between fluorescence and standard parameters.
• Results have shown high correlation between fluorescence values (peaks T and C) and BOD, COD and TOC. Similar correlation was observed for both filtered and unfiltered samples.
• The flow trials showed a strong correlation between fluorescence and BOD, and effective fluorescence response to changes in the ASP efficiency.
• Regarding the real-time experiment, fluorescence spectroscopy proved to be a robust technique as it was able to detect minor changes in effluent quality caused by differences in influent quality and minor events at the treatment works.

This project has helped identify the advantages and limitations in applying the technique for wastewater quality assessment. Nevertheless, fluorescence spectroscopy proved to be a sensitive technique for on-line monitoring of treatment efficiency.

Impact of project results
It is anticipated that the project results will have great impact on the research community and wastewater treatment industry. The outcomes of SO1 challenge the current views on the relationship between fluorescence and standard parameters. Therefore, the paper that will be published based on these results will attract the attention of the scientific community. This could potentially help researchers to develop better strategies for implementing fluorescence spectroscopy in water quality monitoring.
The studies demonstrated that portable fluorometers could successfully be used to monitor the wastewater treatment efficiency. In particular, submersible devices are recommended due to limited maintenance procedures and simple operation. Therefore, wastewater operators could easily use submersible fluorometers to check the effluent water quality without extensive training.
Impact of Marie Curie Fellowship on Dr. Carstea’s career
After the completion of the fellowship, Dr. Carstea has returned to her home institution, where she has submitted an application for promotion. Following her successful career stages she will be promoted to a senior researcher position. Furthermore, Dr. Carstea has the opportunity to develop her own laboratory for water quality studies, as part of a large national project proposal for infrastructure development. If the proposal is successful she will be the leader of the laboratory allowing her to develop her own water quality group.