Energy and carbon footprints of sewage treatment methods.

The paper presents energy and carbon footprints of sewage treatment plants (STPs) operating at different scales and using different technology options based on primary data from 50 STPs operating in India and the UK. The study used a combination of fundamental mass-balance approach for energy consumption and the methodology defined by IPCC for the carbon emissions. Small-scale institutional STPs consume twelve times the energy consumed by large-scale municipal STPs, the corresponding energy intensities being 4.

Fate of Trace Metals in Anaerobic Digestion.

A challenging, and largely uncharted, area of research in the field of anaerobic digestion science and technology is in understanding the roles of trace metals in enabling biogas production. This is a major knowledge gap and a multifaceted problem involving metal chemistry; physical interactions of metal and solids; microbiology; and technology optimization. Moreover, the fate of trace metals, and the chemical speciation and transport of trace metals in environments--often agricultural lands receiving discharge waters from anaerobic digestion processes--simultaneously represents challenges for environmental protection and opportunities to close process loops in anaerobic digestion.

Determination of changes in wastewater quality through a treatment works using fluorescence spectroscopy.

Fluorescence spectroscopy was used to characterize municipal wastewater at various stages of treatment in order to understand how its fluorescence signature changes with treatment and how the signal relates to biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The impact of size fractionation on the fluorescence signal was also investigated. Fluorescence measurements were taken for unfiltered and filtered (0.

Velocity gradient as a tool to characterise the link between mixing and biogas production in anaerobic waste digesters.

Whilst the importance of mixing in anaerobic digesters to enhance process performance and gas production is well recognised, the specific effects of mixing regime on biogas production are not clear. Here, the velocity gradient is used to demonstrate the importance of minimally mixed zones in a digester, with computational fluid dynamics (CFD) models indicating that 20-85% of a laboratory-scale digester experiences local velocity gradients of less than 10 s⁻¹, dependent on mixing speed. Experimental results indicate that there is a threshold above which increased mixing speed (and hence velocity gradient) becomes counter-productive and biogas production falls.

A novel laboratory method to determine the biogas potential of iron-dosed activated sludge.

Sludge biogas potential is often reduced by iron-dosing, the extent of the reduction being related to the nature of the sludge and the dosing process. The aim of this research was to develop a rapid laboratory method to measure the impact of iron-dosing on the biogas potential of activated sludge, taking into account the mechanisms that may be decreasing biogas yield. To validate the method, sequential extraction (SE) was used to fractionate iron and phosphorus in the sludge before and after iron-dosing.

The digestibility of iron-dosed activated sludge.

The impact of chemical phosphorus (P) removal on anaerobic digestion (AD) has long been debated, possibly because there is no general consensus of the definition of impaired AD, but also because of the different assessment methods used. This research surveyed 12 wastewater treatment plants to compare the relative digestibility of iron-dosed with undosed activated sludge during two batch test trials. Results showed that iron-dosed sludge negatively impacted AD by reducing the volume of biogas (12%) and methane (5.

Can fluorescence spectrometry be used as a surrogate for the Biochemical Oxygen Demand (BOD) test in water quality assessment? An example from South West England.

The fluorescence intensities of tryptophan-like, tyrosine-like and humic-like materials were determined using excitation-emission-matrices (EEMs) for a wide range of samples including natural surface waters, sewage and industrial effluents and waters that have experienced known pollution events from the South West of England (n=469). Fluorescence intensities reported in arbitrary fluorescence units (AFU) were correlated with standard five day Biochemical Oxygen Demand (BOD(5)) values which were used as an indicator of the amount of biodegradable organic material present. Tryptophan-like fluorescence, which has been found to relate to the activity of the biological community, showed the strongest correlation with BOD(5).

Addition of Al and Fe salts during treatment of paper mill effluents to improve activated sludge settlement characteristics.

Metal salts, ferrous sulphate and aluminium chloride, were added to laboratory-scale activated sludge plant treating paper mill effluents to investigate the effect on settlement characteristics. Before treatment the sludge was filamentous, had stirred sludge volume index (SSVI) values in excess of 300 and was moderately hydrophobic. The use of FeSO4.

An examination of the treatment of iron-dosed waste activated sludge by anaerobic digestion.

Anaerobic digestion is an important sludge treatment process enabling stabilisation of the organic fraction of sewage sludge prior to land application. Any practice which might retard the anaerobic digestion process will jeopardize the stability of the resulting digested sludge. This paper reports on an investigation into the relative digestibility of iron-dosed waste activated sludge (WAS) from a sewage treatment works (STW) with chemical phosphorus removal (CPR), in comparison to WAS from a works without phosphorus removal.

Measuring metal and phosphorus speciation in P-rich anaerobic digesters.

High concentrations of soluble orthophosphate, magnesium and potassium are released during anaerobic digestion of biological phosphorus removal (BPR) sludge. This research was undertaken to investigate the effects of phosphorus enrichment on digester performance, metal and phosphorus speciation. High concentrations of soluble PO4-P (> 250 mg/l) were found to have a retarding effect on anaerobic digestion, reducing the rate of volatile solids digestion and methane production in comparison to control digesters.