Improved design and performance of continuous thickeners should be achieved through a better understanding of the sludge transport processes involved and the variability of sludge thickenability. A software package called PHOENICS was used to model the three-dimensional flow of sludge in the transport zone of a 20m diameter thickener. A mass transport efficiency was evaluated to test the efficacy of the ploughing system, and tracer simulations were performed to study the degree of back-mixing induced. Interpretation of the results suggests that:○Optimum orientation of the ploughs to the radial arm is 60° to 70°.○Transport of sludge to a central outlet occurs principally in the wake of the advancing ploughs, and that ploughs are less efficient than conventional theories dictate.○Sludge in the ploughing zone is mixed, thus potentially impairing thickener performance. The thickenability of mixed raw sludge arising at a large activated sludge works was monitored. Pronounced seasonal variations were observed, with a marked deterioration in thickenability in late summer and autumn. These were confirmed in trials of a 20m diameter continuous thickener. Consequently the proposed thickening strategy for this works has been revised.

Pilot plant studies were conducted to evaluate the use of pre-denitrification for nitrogen removal at low-rate biological filter works. The plant was operated over a range of recycle ratios to determine the optimum operating conditions. It was possible to meet a total nitrogen limit of 15 mg TN/l with a 2:1 ratio of recycled filter effluent to settled sewage. Following the studies, an economic comparison was made to compare the costs of pre-denite plant with post-denitrification in tertiary sand filters. The cost-effectiveness of the pre-denite process depended on the price of the external carbon source used in post-denite plant. Biological fluidised beds were shown to be the most cost-effective type of pre-denite plant.

Introduction:Healthcare-associated infections (HAIs) are an important, potentially preventable reason to maintain a clean healthcare environment. However, guidelines from Europe and North America do not concur—European guidelines recommend using neutral detergent (followed by chlorine-based disinfection (CBD) if required), whilst North American guidelines recommend using detergent or hospital-grade disinfectant-detergents for routine cleaning or decontamination of noncritical healthcare environmental surfaces. The objective of this study was to compare the effectiveness on rates of HAIs of: (i) disinfectant-detergents versus detergents; and (ii) the active ingredient of many disinfectant-detergents—quaternary ammonium compounds (QAC)—versus CBD.Methods:A rapid review of systematic reviews was conducted using the following search terms: keywords and controlled vocabulary terms for the concepts of “healthcare environmental surfaces” AND (“QAC-based disinfectants” OR “disinfectant-detergents” OR “decontamination”) AND (“environmental contamination” OR “colonization” OR “HAIs”). The search filters included systematic reviews, guidelines, and technology reports. The following databases were searched: The Cochrane Library; PubMed; and health technology assessment and guideline websites for gray literature. Systematic reviews of studies comparing the effects of disinfectant-detergents with detergent, or comparing QAC with CBD, on rates of HAIs in the healthcare environment were included. Reviews on the cleaning or disinfection of body surfaces or disinfection of invasive medical devices were excluded. Quality assessment was not conducted. Data extraction was performed using a pro forma.Results:The literature search resulted in 356 titles. From ninety-four potentially relevant abstracts, fifty-seven full-texts were evaluated: fifty-one were excluded (eight non-English) and six were included. All review authors cautioned that the evidence was low level, methodologically poor, subject to confounding, and didn't address adverse outcomes. The reviews identified eight relevant primary studies, three of which compared disinfectant-detergents with detergent and found no difference in rates of HAI. Five studies compared QAC with CBD. All five demonstrated that CBD was superior to QAC and reduced Clostridium difficile infection rates in outbreak contexts. Furthermore, QAC may induce sporulation and microbial resistance.Conclusions:Low-level evidence suggested that: there is no advantage in using disinfectant-detergents for routine cleaning of noncritical surfaces; CBD is superior to QAC-based disinfection in reducing clostridial infections; and QAC agents may induce sporulation or microbial resistance.

Consolidation is potentially the most cost‐effective of all sludge treatment processes. However, traditional design procedures have been oversimplified such that the process has not generally been fully exploited. The objective of this report is to summarize the Water Research Centre (WRc) procedure for sizing sewage sludge consolidation tanks, and explain the major design aspects which control the effective operation of the plant. The procedure provides a means of sizing tanks to consolidate any particular sewage sludge to any solids concentrations up to the maximum, and is applicable to both the batch and continuous operational modes. To obtain the predicted performance, the essential equipment such as the picket fence and control system, comprising a consolidation plant, must be suitably designed.

The efficacies of 2 new teat dip formulations were tested against experimental challenge by contagious mastitis pathogens Staphylococcus aureus and Streptococcus agalactiae over a 12-wk period. Formulations contained an iodine complex (0.5 or 1.0% iodine) and skin conditioning agents (propylene glycol, polyvinylpyrridone, glycerine, lanolin, allantoin, and aloe). Percentage reduction (dipped vs. control mammary quarters) in new contagious mastitis pathogen intramammary infections for the 0.5 and 1.0% iodine dips was 65.4 and 84.5, respectively. Both dips were significantly effective in reducing new contagious intramammary infections. Teat skin scores and teat end scores varied over time but were virtually identical for both treated and control teats, for both treatments. Thus, both dips were effective in reducing new contagious mastitis infections without untoward effects on teat skin condition.