During advanced biological wastewater treatment, a huge amount of sludge is produced as a by-product of the treatment process. Hence, reuse and recovery of resources and energy from the sludge is a big technological challenge. The processing of sludge produced by Wastewater Treatment Plants (WWTPs) is massive, which takes up a big part of the overall operational costs. In this regard, anaerobic digestion (AD) of sewage sludge continues to be an attractive option to produce biogas that could contribute to the wastewater management cost reduction and foster the sustainability of those WWTPs. At the same time, AD reduces sludge amounts and that again contributes to the reduction of the sludge disposal costs. However, sludge volume minimization remains, a challenge thus improvement of dewatering efficiency is an inevitable part of WWTP operation. As a result, AD parameters could have significant impact on sludge properties. One of the most important operational parameters influencing the AD process is temperature. Consequently, the thermophilic and the mesophilic modes of sludge AD are compared for their pros and cons by many researchers. However, most comparisons are more focused on biogas yield, process speed and stability. Regarding the biogas yield, thermophilic sludge AD is preferred over the mesophilic one because of its faster biochemical reaction rate. Equally important but not studied sufficiently until now was the influence of temperature on the digestate quality, which is expressed mainly by the sludge dewateringability, and the reject water quality (chemical oxygen demand, ammonia nitrogen, and pH). In the field of comparison of thermophilic and mesophilic digestion process, few and often inconclusive research, unfortunately, has been published so far. Hence, recommendations for optimized technologies have not yet been done. The review presented provides a comparison of existing sludge AD technologies and the gaps that need to be filled so as to optimize the connection between the two systems. In addition, many other relevant AD process parameters, including sludge rheology, which need to be addressed, are also reviewed and presented.

Selenium is an essential element since it is necessary for metabolism and is also toxic to the living things if it is consumed above the desirable limit. For instance, up to 40 µg per d of dietary selenium is essential for human health; however, consumption of a little over 400 µg per d could result in adverse physiological problems. In the environment, selenium occurs in different species; of which selenate and selenite are its most toxic forms accounting for 95% of selenium toxicity. Though, selenium fortification is important for normal human physiology in selenium deficient environments, it needs to be minimized or removed from selenium rich environmental media. Thus, its quantification is significantly important to control per limit. Currently there is advancement in the detection and quantification of selenium in environmental including the use of a Hydride Generating Atomic Absorption Spectroscopy. Due to the excess occurrences of selenium in different locations the removal techniques from geogenic or anthropogenic sources include microbial metabolism, phytoremediation, sorption, membrane separation, coagulation, ion exchange and catalytic reduction. Most of all, the microbial removal is applied in drinking water supply and in selenium recovery from wastewater sludge. Though current selenium removal from sorption studies reported better efficiency, phytoremediation appears attractive due to its field scale application advantage. However, the fate of selenium following phytoremediation remains unaddressed.

Recently, water scarcity, world population rise and urbanization are causing desalting of seawater. Membrane separation processes such as reverse osmosis are applied for desalination over the conventional mass transfer techniques. For instance, reverse osmosis accounts for the treatment of nearly 1% of the world water supply and its applications are increasing with time. However, cost, technical management and efficiency are challenging aspects. Hence, membrane fouling, direct and indirect investment costs, and permeate quality are the major hurdles encountered. Toward solving these problems, various studies are being conducted including varying membrane operating conditions and separation methodologies whereby ion-exchange–reverse osmosis hybrids and the coupling of two or more other membrane filtration techniques can be mentioned. Apparently, most of the hybrid techniques targeted for the selective removal of a pollutant. Hence, ion exchange–reverse osmosis is the most applied hybrid process particularly for boron removal due to its public and environmental health impact. Despite that, there is no current and comprehensive review that bridged the piece by piece and fragmented reports. In this review, desalination–ion-exchange coupling with other membrane filtration is explored in detail and the recent advances in composite membrane material synthesis are uncovered. Further, the status, cost and future potential of hybrid membranes are discussed and gaps are identified for future research.

This study was conducted to determine the occupational risks of cleaners of healthcare institutions like Tikur Anbassa Specialized Referral Hospital, Addis Ababa, Ethiopia. A cross-sectional study was conducted to assess the knowledge, attitude and practice of cleaners focusing on occupational health and safety issues, including biological and chemical risks. Interview data were collected using a structured questionnaire that involved all the cleaners. Additionally, focus group discussions and use of observational checklists were applied to capture both administrative and the actual waste management aspects. The result of the study showed that all cleaners had a favorable attitude towards safety principles. However, the knowledge of cleaners on occupational safety was so poor to the level that all of them did not even know the meaning of nosocomial infection. Almost all of the cleaners, 69 (98.6%), had not taken any preemployment training by the time of the interview. All of the cleaners’ practices were not fully compliant with the universal precaution principles and the major proportion, 37 (53%), of them had instances of needlestick injuries ranging from one to four times. Furthermore, the wastes in the hospital were located indiscriminately and with an uncovered container. Though cleaners had a desirable attitude, the status of occupational safety awareness and practice were not to the expected level that it should be. This institution, and similar institutions, should give emphasis to occupational safety issues with healthcare waste management. Awareness training has to be given before employment as well as refreshment trainings after engagement.