ERTDI Report 60 - J. Marchesi et al.
Summary: Final report for the ERTDI project 2001-LS-FW2-M1 by Julian Marchesi, Niall O’Leary, Jill Kirby, Margaret Toomey and Alan Dobson
This project set out to examine the use of biological-based approaches to facilitate the removal of nutrients, particularly phosphates, from food processing waste streams. The work aimed to develop biological management procedures, incorporating molecular-based methodologies to assess the performance of biological nutrient removal (BNR) systems treating these food wastes. To this end, culture-independent molecular-based approaches have been employed to show that in laboratory-scale enhanced biological phosphate removal (EBPR) processes significant changes in the overall microbial community structures can be linked to a failure to efficiently remove phosphate. From this work, it appears that the key factors that influence decreases in phosphate removal efficiency are likely to be changes in the influent composition and, in particular, the quality and quantity of short-chain fatty acids (SCFAs). While further work will need to be undertaken, it appears that the control of influent quality may be a key factor to aid in the successful removal of phosphate by EPBR systems and failure to ensure sufficient levels of SCFAs may be a contributory factor in their malfunctioning.
This project also set out to investigate the use of low pH ‘shock’ as a novel method to remove phosphate from food processing waste streams. Work with synthetic waste streams and laboratory-scale bioreactors operating at a low pH indicated that acidification of the influent to pH 5.2 had the effect of achieving a low reactor pH with a concomitant 50% phosphate removal. Molecular-based approaches identified a number of microbial strains from genera that have recently been reported as having a crucial role in phosphate removal in several activated sludge environments. It is clear, however, that if the low pH ‘shock’ approach is to be useful it will be important to achieve microbial control in feed reservoirs via reduced pH. If influent nutrient concentrations are contaminated particularly with lactose-utilising micro-organisms, then it is likely that insufficient chemical oxygen demand (COD) may be present in the reactor to maintain the sludge sufficiently to promote effective phosphate removal. Future research in this ‘acid shock’ area should investigate the potential to acclimatise sludges with increasing COD concentrations. It is, however, likely that the treatment of industrial waste-water COD will require the incorporation of a pre-EBPR reactor sludge-exposure step to mimic, in a controlled fashion, the effects of reservoir contamination which we have observed in this study.
The project also set out to ascertain, using compost-quality testing standards, whether sludge generated from biological phosphate removal (BPR) could be composted to a satisfactory quality. The project succeeded in establishing and standardising a number of tests and methods to assess compost quality and subsequently evaluated these methods in laboratory-scale test compost units. These methods included inductively coupled plasma–mass spectrometry (ICP-MS), total Kjeldahl nitrogen determination and most probable number (MPN) analysis. Analysis of the laboratory-scale test compost units showed the benefits of monitoring the process using the validated testing methods.
Finally, the project set out to study the performance of a pilot-scale BNR system, operating under a variety of different conditions. This study found the pilot-scale system capable of treating the elevated nitrogenous loading to the plant during the peak season and also capable of performing reliably in the colder off-peak season. Reductions in the size of the anaerobic and anoxic zones, relative to the total size of the mixed reactor zones, together with reductions in the ratio of return activated sludge to influent flow rate, were found to have a beneficial effect on the BNR process, with the activity of the bacteria within the system in terms of COD, NH4-N and P removal being enhanced by these reductions.
