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Turbidity in water can be caused by a range of different turbidity causing materials (TCM). Here the characteristics and attachment of bacteria to TCMs was assessed and the resultant impact on UV disinfection determined. TCMs represent potential vehicles for bacterial penetration of water treatment barriers, contamination of potable supplies and impact on subsequent human health. The TCMs under investigation were representative of those that may be present in surface and ground waters, both from the source and formed in the treatment process. The TCMs were chalk, Fe (III) hydroxide precipitate, kaolin clay, manganese dioxide and humic acids, at different turbidity levels representative of source waters (0, 0.1, 0.2, 0.4, 1, 2, and 5 NTU). Escherichia coli and Enterococcus faecalis attachment followed the order of Fe(III) > chalk, with little to no attachment seen for MnO2, humic acids and clay. The attachment was postulated to be due to chalk and Fe(III) particles having a more neutral surface charge resulting in elevated aggregation with bacteria compared to other TCMs. The humic acids and Fe(III) were the TCMs which influenced inactivation of E. coli and E. faecalis due to decreasing UV transmittance (UVT) with increasing TCM concentration. The presence of the Fe(III) TCM at 0.2 NTU resulted in the poorest E. coli inactivation, with 2.5 log10 reduction at UV dose of 10 mJ cm− 2 (kd of − 0.23 cm2 mJ− 1) compared to a 3.9 log10 reduction in the absence of TCMs. E. faecalis had a greater resistance to UV irradiation than E. coli for all TCMs. Effective disinfection of drinking water is a priority for ensuring high public health standards. Uniform regulations for turbidity levels for waters pre-disinfection by UV light set by regulators may not always be appropriate and efficacy is dependent on the type, as well as the amount, of turbidity present in the water.

The naphthoic acids are challenging and costly to remove from water and soil. 1-Hydroxy-2-Naphthoic acid (HNA) is a phenanthrene decomposition product from petroleum-contaminated environments during the aerobic decomposition of polyaromatic hydrocarbons. The hydrogeological mobility of hydrocarbon breakdown products represent a pollution risk (e.g. for drinking water sources). Adsorption to biochar produced from agricultural by-products is a useful strategy to remediate contaminated wastewaters. Here, we examine the controls on the HNA adsorption to the adsorbents magnetite, clay minerals, biochar and magnetite enriched companion materials, namely the influence of contact time, contaminant concentration and ionization effects at different pH. The adsorption of HNA was investigated using low-cost and readily available adsorbents: (i) wheat straw biochar, (ii) rice husk biochar, (iii) sugarcane biochar, (iv) zeolite, (v) montmorillonite, (vi) magnetite and their enriched magnetic companions. Magnetite enriched biochar exhibited greater adsorption rates compared with their nonmagnetic analogs for HNA. The maximum adsorption capacity of the magnetite enriched compounds (initial water concentration of 0.32 mmol HNA.L − 1 ) was 0.45 mmol.HNA.g − 1 of enriched zeolite. The magnetite enriched biochar and conventional biochar showed similar adsorption kinetics although magnetite enrichment improved the efficacy of adsorption. The adsorption fitted the pseudo-second order model in all cases, suggesting the dominant mechanism of adsorption was chemisorption. The magnetite enrichment reduced intra-particle diffusion, possibly due to fouling or blocking of pores within the particles, as evidenced by the decrease in diffusion rate constants. Overall, HNA adsorption improved after magnetic enrichment due to magnetite competing with inhibition sites on the biochar carriers. These findings translate into equivalence between magnetite and magnetic biochars, suggesting cheaper alternative materials could be synthesized in situ with the biochar acting as both an adsorbent and carrier, increasing the prospect of designer biochars for targeted pollutant removal. This approach has the potential to be used for wastewater treatment or for application as a soil additive for remediation of runoff from contaminated soils.

Biological processes for wastewater treatment is limited by extracellular enzyme activity (EEA) of the biofilm on polymeric substrates. The efficiency of biodegradation / biosorption mechanisms causing EEA and organic load removal in biofilms remains unknown. Our hypothesis was that the limiting step of biological process can be overcome by biostimulation and/or bioaugmentation of the return sludge in hybrid biofilm reactors, which leads to competition between suspended and attached bacteria and lower effective substrate to microrganism ratio. Therefore, we considered more active biosolids to perform best at enhancing reactor removal rate. To test this, the efficacy of recycling distinct bio-solids types considered to have different bacterial activity such as final effluent (FE), humus solids (HS) and recycle activated sludge (RAS) on performance improvements of rotating biofilm reactors (RBRs). These bio-solids were investigated under high organic loading rates (OLR) and solids loading rates (SLR) using pilot scale reactors receiving real municipal wastewaters. Controlled overloading of RBRs revealed that EEA improved with increasing OLR/SLR. High SLR (>3.3 kg Total Suspended Solids m−2 d−1) delayed and decreased the reduction of organic and inorganic removal rates in the biological processes which commonly occurs under high OLRs. This effect was more pronounced in the highest activity solids (RAS > HS > FE) suggesting the activity and function of bio-solids was critical to improve performance of RBRs. High OLR and SLR induced efficient denitrification and organics removal within the biofilm reactor at residence times of

Ammonia oxidising microorganisms (AOM) play an important role in ammonia removal in wastewater treatment works (WWTW) including rotating biological contactors (RBCs). Environmental factors within RBCs are known to impact the performance of key AOM, such that only some operational RBCs have shown ability for elevated ammonia removal. In this work, long-term treatment performance of seven full-scale RBC systems along with the structure and abundance of the ammonia oxidising bacteria (AOB) and archaea (AOA) communities within microbial biofilms were examined. Long term data showed the dominance of AOB in most RBCs, although two RBCs had demonstrable shift toward an AOA dominated AOM community. Next Generation Sequencing of the 16S rRNA gene revealed diverse evolutionary ancestry of AOB from RBC biofilms while nitrite-oxidising bacteria (NOBs) were similar to reference databases. AOA were more abundant in the biofilms subject to lower organic loading and higher oxygen concentration found at the distal end of RBC systems. Modelling revealed a distinct nitrogen cycling community present within high performing RBCs, linked to efficient control of RBC process variables (retention time, organic loading and oxygen concentration). We present a novel template for enhancing the resilience of RBC systems through microbial community analysis which can guide future strategies for more effective ammonia removal. To best of the author’s knowledge, this is the first comparative study reporting the use of next generation sequencing data on microbial biofilms from RBCs to inform effluent quality of small WWTW. Keywords: Biofilm, Rotating biological contactor, Nitrification, Wastewater treatment, Ammonia oxidising bacteria, Ammonia oxidising archaea