Comparing the performance of aerobic granular sludge versus conventional activated sludge for microbial log removal and effluent quality: Implications for water reuse.

The application of aerobic granular sludge (AGS) technology has increased in popularity, largely due to the smaller physical footprint, enhanced biological nutrient removal performance and ability to perform with a more stable operation when compared to conventional activated sludge (CAS) systems. To date, the ability of AGS to remove microbial pathogens such as; Escherichia coli, Giardia, and Cryptosporidium has not been reported. This study compared the log10 removal performance of commonly used pathogen surrogates (sulfite-reducing clostridia spores, f-RNA bacteriophage, E. coli and total coliforms) by AGS and CAS during the start-up phase, through to maturation. Results showed that AGS performed as well as CAS for the log10 removal performance of all microbial surrogates, except for spores which were removed more effectively by AGS most likely due to greater adherence of spores to the AGS biomass compared to CAS mixed liquor. Results suggest that AGS is capable of meeting or exceeding CAS-equivalent health-based targets for pathogen removal in the context of water recycling as well as not adversely affecting the secondary effluent water quality (suspended solids, turbidity and particle size) in terms of ultraviolet light transmissivity (254 nm). These findings confirmed for the first time that the adoption of AGS operation would not adversely impact downstream tertiary disinfection processes from altered water quality, nor would it require further pathogen treatment interventions in addition to what is already required for CAS systems.

Ecology and performance of aerobic granular sludge treating high-saline municipal wastewater.

The successful development of aerobic granular sludge (AGS) for secondary wastewater treatment has been linked to a dedicated anaerobic feeding phase, which enables key microbes such as poly-phosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms to gain a competitive advantage over floc-forming organisms. The application of AGS to treat high-saline sewage and its subsequent impacts on microbial ecology, however, are less well understood. In this study, the impacts of high-saline sewage on AGS development, performance and ecology were investigated using molecular microbiology methods. Two feeding strategies were compared at pilot scale: a full (100%) anaerobic feed; and a partial (33%) anaerobic feed. The results were compared to a neighbouring full-scale conventional activated sludge (CAS) system (100% aerobic). We observed that AGS developed under decreased anaerobic contact showed a comparable formation, stability and nitrogen removal performance to the 100% anaerobically fed system. Analysis of the microbial ecology showed that the altered anaerobic contact had minimal effect on the abundances of the functional nitrifying and denitrifying bacteria and Archaea; however, there were notable ecological differences when comparing different sized granules. In contrast to previous work, a large enrichment in PAOs in AGS was not observed in high-saline wastewater, which coincided with poor observed phosphate removal performance. Instead, AGS exhibited a substantial enrichment in sulfide-oxidising bacteria, which was complemented by elemental analysis that identified the presence of elemental sulfur precipitation. The potential role for these organisms in AGS treating high-saline wastewater is discussed.

Evaluating membrane performance in recycled water treatment plants for assets replacement strategy.

Membranes are an important barrier used in recycled water treatment plants for pathogen removal. Understanding performance over operational life is important to inform membrane replacement. In this study, full scale virus challenge testing was conducted on newly commissioned membranes to validate virus log removal values for accreditation. After six years of operation, the membrane integrity was repeated to ensure compliance with the state regulatory health authority and gain an understanding of the asset's condition. Membrane performance was assessed using a combination of complementary tests including membrane autopsy and chemical tolerance testing to assess individual modules and selected membrane fibres, followed by a full scale virus challenge for whole of unit assessment. The results demonstrated that the aged membrane fibres were intact and had not been affected by long-term exposure to chlorine, which provides valuable information for membrane asset replacement strategies.

Fate of cyanobacteria in drinking water treatment plant lagoon supernatant and sludge.

In conventional water treatment processes, where the coagulation and flocculation steps are designed to remove particles from drinking water, cyanobacteria are also concentrated into the resultant sludge. As a consequence, cyanobacteria-laden sludge can act as a reservoir for metabolites such as taste and odour compounds and cyanotoxins. This can pose a significant risk to water quality where supernatant from the sludge treatment facility is returned to the inlet to the plant. In this study the complex processes that can take place in a sludge treatment lagoon were investigated. It was shown that cyanobacteria can proliferate in the conditions manifest in a sludge treatment lagoon, and that cyanobacteria can survive and produce metabolites for at least 10days in sludge. The major processes of metabolite release and degradation are very dependent on the physical, chemical and biological environment in the sludge treatment facility and it was not possible to accurately model the net effect. For the first time evidence is provided to suggest that there is a greater risk associated with recycling sludge supernatant than can be estimated from the raw water quality, as metabolite concentrations increased by up to 500% over several days after coagulation, attributed to increased metabolite production and/or cell proliferation in the sludge.

Effect of feed starvation on side-stream anammox activity and key microbial populations.

The anaerobic ammonium oxidation (anammox) process is widely acknowledged to be susceptible to a wide range of environmental factors given the slow growth rate of the anammox bacteria. Surprisingly there is limited experimental data regarding the susceptibility of the anammox process to feed starvations which may be encountered in full-scale applications. Therefore, a study was established to investigate the impact of feed starvations on nitritation and anammox activity in a demonstration-scale sequencing batch reactor. Three starvation periods were trialled, lasting one fortnight (15 d), one month (33 d) and two months (62 d). Regardless of the duration of the starvation period, assessment of the ammonia removal performance demonstrated nitritation and anammox activity were reinstated within one day of recovery operation. Characterisation of the community structure using 16S rRNA and functional genes specific for nitrogen-related microbes showed there was no clear impact or shift in the microbial populations between starvation and recovery phases.

Extraction method for total microcystins in cyanobacteria-laden sludge.

Cyanobacteria in water treatment sludge pose a health risk as they continue to be viable, multiply, and produce potentially harmful secondary metabolites. To date, little research has focused on accurately determining cell bound microcystin (MC) concentrations of cyanobacterial cells in water treatment sludge. Three extraction methods (freeze-thaw, lyophilisation, direct methanolic extraction) with three different pre-treatments (homogenisation, (ultra)sonication, combination of both, and controls) were investigated for their MC extraction recovery. It was found that lyophilisation with prior sonication achieved the highest toxin recovery across the two MC analogues (MC-LR, MC-LA) tested. The method was able to extract 69 and 56% of MC-LR and MC-LA, respectively with good reproducibility. Comparable results were also obtained with direct methanolic extraction, with poor reproducibility. The least efficient method was freeze-thawing which achieved poor recoveries and was less reproducible. This study highlights a rapid, efficient, low-cost extraction method for determining total microcystins in cyanobacterial-laden sludge.