Search

The safe management of fecal sludge from the 3.4 billion people worldwide that use onsite sanitation systems can greatly reduce the global infectious disease burden. However, there is limited knowledge about the role of design, operational, and environmental factors on pathogen survival in pit latrines, urine diverting desiccation toilets, and other types of onsite toilets. We conducted a systematic literature review and meta-analysis to characterize pathogen reduction rates in fecal sludge, feces, and human excreta with respect to pH, temperature, moisture content, and the use of additives for desiccation, alkalinization, or disinfection. A meta-analysis of 1,382 data points extracted from 243 experiments described in 26 articles revealed significant differences between the decay rates and T99 values of pathogens and indicators from different microbial groups. The overall median T99 values were 4.8 days, 29 days, >341 days, and 429 days for bacteria, viruses, protozoan (oo)cysts, and Ascaris eggs, respectively. As expected, higher pH values, higher temperatures, and the application of lime all significantly predicted greater pathogen reduction rates but the use of lime by itself was more effective for bacteria and viruses than for Ascaris eggs, unless urea was also added. In multiple lab-scale experiments, the application of urea with enough lime or ash to reach a pH of 10 – 12 and a sustained concentration of 2,000 – 6,000 mg/L of non-protonated NH3N reduced Ascaris eggs more rapidly than without urea. In general, the storage of fecal sludge for 6 months adequately controls hazards from viruses and bacteria, but much longer storage times or alkaline treatment with urea and low moisture or heat is needed to control hazards from protozoa and helminths. More research is needed to demonstrate the efficacy of lime, ash, and urea in the field. More studies of protozoan pathogens are also needed, as very few qualifying experiments were found for this group.

We assessed the physicochemical and microbiological properties of composting toilet products in Abidjan for their potential use in agriculture. Samples of urine and faeces were collected and analysed after 123 days of storage in plastic cans (urine) and 8 months of storage in closed composting bags (faeces). Selected physicochemical parameters (ammonium, phosphorus, potassium, calcium, magnesium) and pathogens (bacteria and helminths eggs) were monitored. Results showed that temperature and pH values were 26.0°C and 7.2, and 27.6°C and 8.6 for the faeces and urine, respectively. The physicochemical analysis revealed high nutrient contents and low trace metal levels in the faeces-based compost. Concentrations of magnesium, cadmium, copper, lead and zinc ranged from 0.46 to 54.98 mg/kg; while those of phosphorus, potassium and calcium were >700 mg/kg on average. In urine, the concentrations of phosphorus, potassium, calcium, copper and zinc were 930, 1240, 1402.8, 0.0672 and 0.121 mg/L, respectively. Various bacteria (including total coliforms, faecal coliforms, faecal streptococci and anaerobic sulphite reducers), along with Ascaris lombricoïds (1.66 eggs/g), were found in the faeces-based compost. Our findings indicate that the faeces-based compost was not homogeneous, namely with regard to the microbiological parameters, and additional time would be necessary to bring it to stability. [ABSTRACT FROM AUTHOR]

One of the most undesired wastes is the human excreta due to the socio-environmental pressure. Otherwise, the nutriments contained in human excreta could be used as fertilizers to enrich the soil. Familial waterless litter composting toilets (FWLCT) are an alternative for locations where a centralized sewerage network cannot be provided or where there is a lack of standard urban infrastructure including roads, electricity, and water supply. The scientific researches on the composting techniques, the methods of control of the composting processors, and the rate of produced leachate are very limited. In this research, the composting systems included a feces and urine collection device. In each passage, the litter (carbonaceous material) is added to the excreta. Regularly, the buckets were emptied into a composting device located outside the house to which an additional portion of carbonaceous materials can be added. Monitoring was carried out on five rural and one urban familial composting areas in France for 1.5 years. The physiochemical and microbiological properties of the compost and leachate have been monitored and measured in compliance with the protocols. The results show that one of the main problems of this system of human excreta treatment is that the composting process does not achieve a significant rise in temperature and does not allow reaching the optimum temperatures (> 50 °C). Otherwise, from an agronomic point of view, the obtained compost is not rich enough in nutriments to be a good compost as soil fertilizer. But it can be used as a soil conditioner. The average leachate flux from the composters is 1.79 L/day. Because of the very short stay time in the piles, the leachate is contaminated by harmful bacteria and should be treated by another sanitation system. [ABSTRACT FROM AUTHOR]

Several studies on sustainable technologies for the built environment (e.g., green roofs, green walls, etc.) have been carried out. Many of these focus on the technical performance of such technologies. Nonetheless, it also becomes necessary to examine how the public perceives such technologies. This understanding is clearly important to support their widespread use. More specifically, such perception can be incorporated into product design to increase people's acceptance. The contribution of this paper is twofold. First, it presents results of a survey examining the perception of people from a small city in the Southern region of Brazil (Feliz, RS) regarding three sustainable technologies: green roofs, green walls, and composting (or dry) toilets. Second, it proposes a set of preliminary design guidelines to improve acceptance of more sustainable technologies based on people's perception: (1) make the technology look good; (2) make visible the benefits provided by the technology; and (3) design the technology to avoid misunderstandings and concerns. [ABSTRACT FROM AUTHOR]

The study was carried out to assess the efficacy of a standard Biofil toilet digester with regard to its effluent quality and to evaluate the performance of new effluent polishing options being developed by BiofilCom. Influent and effluent were collected from 18 standard Biofil digesters connected to full-flush toilets. Effluent from five pilot installations with improved effluent polishing options were also taken for analyses. Ten other Biofil installations were selected to assess the impact of digester effluent discharge on the surrounding soil. Pollutant concentrations in the Biofil effluent exceeded both Ghana EPA and WHO standards for discharge though pollutant removal efficiencies were high: 84% for biochemical oxygen demand, 86.1% for chemical oxygen demand and 82.4% for total suspended solids.Escherichiacoliand total coliform levels were significantly reduced by 63% and 95.6%, respectively, and nutrients were the least removed from effluents. Generally, effluents from the majority of the pilot polishing options met most of the discharge standards.E. coliwere present in the soil at all study sites, except one. Biofil digester effluent is discharged subsurface but comparing their effluent quality with standards for discharge into water courses is relevant especially in areas of frequent flooding and high water tables. [ABSTRACT FROM PUBLISHER]

Safe and appropriate disposal of human waste is a basic requirement for sanitation and protection of public health. For proper sanitation and nutrient recovery, it is necessary to ensure effective treatment methods to complete pathogen destruction in excreta prior to reuse. Composting toilets convert faeces to a reusable resource such as fertilizer or humus for organic agriculture. A composting toilet for rural Burkina Faso was created by modifying a commercial model available in Japan to improve hygiene and increase food production. The toilet has shown to result in a degraded final product, but its effectiveness for pathogen destruction was unclear due to low temperatures generated from the toilet. This study aimed to sanitize compost withdrawn from the composting toilet for food production by setting post-treatment conditions. The inactivation kinetics ofAscaris suumeggs, selected as an indicator for helminth eggs, was determined during post-treatment at different temperatures (30°C, 40°C, 50°C and 60°C) with varying moisture contents (MC) (50%, 60% and 70%). The treatment of compost in a possible additional post-treatment after the composting process was tried in the laboratory test. Inactivation ofA. suumeggs was fast with greater than two log reductions achieved within 2 h for temperature 50°C and 50% MC and greater than three log reductions for temperature 60°C and 50% MC within 3 h. Statistical analysis showed the significant impact of temperature and moisture on the inactivation rates ofA. suumeggs. The post-treatment can efficiently increase helminth eggs destruction prior to reuse. [ABSTRACT FROM PUBLISHER]

The safe management of fecal sludge from the 3.4 billion people worldwide that use onsite sanitation systems can greatly reduce the global infectious disease burden. However, there is limited knowledge about the role of design, operational, and environmental factors on pathogen survival in pit latrines, urine diverting desiccation toilets, and other types of onsite toilets. We conducted a systematic literature review and meta-analysis to characterize pathogen reduction rates in fecal sludge, feces, and human excreta with respect to pH, temperature, moisture content, and the use of additives for desiccation, alkalinization, or disinfection. A meta-analysis of 1,382 data points extracted from 243 experiments described in 26 articles revealed significant differences between the decay rates and T 99 values of pathogens and indicators from different microbial groups. The overall median T 99 values were 4.8 days, 29 days, >341 days, and 429 days for bacteria, viruses, protozoan (oo)cysts, and Ascaris eggs, respectively. As expected, higher pH values, higher temperatures, and the application of lime all significantly predicted greater pathogen reduction rates but the use of lime by itself was more effective for bacteria and viruses than for Ascaris eggs, unless urea was also added. In multiple lab-scale experiments, the application of urea with enough lime or ash to reach a pH of 10 - 12 and a sustained concentration of 2,000 - 6,000 mg/L of non-protonated NH 3- N reduced Ascaris eggs more rapidly than without urea. In general, the storage of fecal sludge for 6 months adequately controls hazards from viruses and bacteria, but much longer storage times or alkaline treatment with urea and low moisture or heat is needed to control hazards from protozoa and helminths. More research is needed to demonstrate the efficacy of lime, ash, and urea in the field. More studies of protozoan pathogens are also needed, as very few qualifying experiments were found for this group., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)

A urine diverting composting toilet system is modified for rural areas of Burkina Faso from the system that is commercially available in Japan. The rural model does not have a heat source. It still has some pathogens in the compost after three months of operation and hence requires a post-treatment. In this study, the kinetics inactivation ofEnterococcusandEscherichia coli, selected as an indicator for pathogenic bacteria, was determined during post-treatment at different temperatures (37, 50, and 70°C) with varying moisture contents (50, 60, and 70%). Additionally, the fate of pathogenic bacteria under different lime doses (1.0, 0.5, and 0.1 g) at 60% of moisture content were determined. As a result, bacteria decreased as temperature increased, moisture reduced, and the length of time increased. However, under high temperature the effect of moisture was not significant. With regards to relative resistance of bacteria,Enterococcuswas the most resistant to temperature. For 6 log reduction target to reduce the concentration ofE. coliin compost, post-treatment conditions of 50°C, 50%, and a contact time over 4.5 h are needed or post-treatment conditions of 70°C, 50%, with a contact time of over 20 min are required. ForEnterococcus, to achieve a 6 log reduction, post-treatment conditions of 50°C, 50%, with a contact time of 15 h or 70°C, 50%, with a contact time of over 2.5 h are required. The addition of the higher dose of Ca(OH)2to increase the pH of compost to ≥8.1 was capable of reducing the concentration of pathogenic bacteria. [ABSTRACT FROM PUBLISHER]

The Morris screening sensitivity analysis (SA) has been used to assess how the uncertainty of input parameters influences the output of the CLARA Simplified Planning Tool (CLARA-SPT). To assess the sensitivity of the tool, four hypothetical waste collection and treatment alternatives, which planned to serve 10,000 people, have been proposed and analysed. These alternatives are (A1) dry sanitation with urine diversion dry toilets (UDDTs), (A2) water-aided sanitation with decentralised treatment units, (A3) water-aided sanitation with central technical treatment and (A4) water-aided sanitation with cesspits. The SA was used to identify the influence of two global and 29 technological input parameters on lifetime costs and residual values of sanitation alternatives. The top two important parameters identified for each alternative are: 'type of urine transport' and 'persons using one UDDT' for alternative A1, 'persons served per septic tank' and 'required surface area for vertical flow constructed wetland' for alternative A2, 'daily diesel generator working hours' and 'expected annual growth' for alternative A3 and 'cesspit volume' and 'expected annual growth' for alternative A4. Additionally, the Morris SA identified non-linearity and/or parameter interaction response. The SA of the specified alternatives shows that from the 29 technological parameters investigated, a subset of 14 important parameters need estimates that are more accurate, whereas a subset of 15 noninfluential parameters can be fixed to a certain value. In particular, two parameters (i.e. cesspit volume and persons using one UDDT) that have been internally fixed in the SPT were found to be important and thus should be made available as input parameters to the user. Overall, the study provides guidance for further modification and simplification of the CLARA-SPT. [ABSTRACT FROM AUTHOR]

Urine diverting composting toilets are becoming increasingly popular and are promoted to sanitize human excreta for recycling them into fertilizer. This study aimed to assess the removal and deactivation of intestinal parasites during the composting process. Batch experiments were conducted by composting human feces in an aerobic composting reactor using shea nut shells as bulky matrix. During 60 composting days, the removal of helminthes eggs and protozoa cysts was assessed and compared with the removal of indicator bacteria and pathogenic bacteria. The bacteria were analyzed by the single layer method on selective media and parasites were counted directly by microscope after compost preparation. The viability of helminthes eggs and protozoan cysts was assessed by a staining exclusion dyeing method. At low temperature, desiccation and alkaline pH obtained during the composting process could not completely destroy indicator bacteria while Salmonella sp. was eliminated after 30 composting days. Entamoeba hystolitica cysts were present in feces at a higher concentration (854/g mean) than Ascaris lumbricoides eggs (204/g mean). The composting process had reduced the total number of Ascaris eggs after 35 days while Entamoeba cysts were still present (beyond 54/g cysts) after 60 composting days. There were no viable Ascaris eggs after 30 days while the viability of Entamoeba cysts was still up 31%. In high concentration, Entamoeba cysts had survived stronger than Ascaris eggs during the composting process. Because of the persistence of some pathogens in compost both Ascaris eggs and Entamoeba cysts are good indicators for parasite removal. [ABSTRACT FROM AUTHOR]

As a pilot approach to describe adverse human health effects from alternative decentralized community water systems compared to conventional centralized services (business- as-usual [BAU]), selected chemical and microbial hazards were assessed using disability adjusted life years (DALYs) as the common metric. The alternatives included: (1) composting toilets with septic system, (2) urine-diverting toilets with septic system, (3) low flush toilets with blackwater pressure sewer and on-site greywater collection and treatment for nonpotable reuse, and (4) alternative 3 with on-site rainwater treatment and use. Various pathogens (viral, bacterial, and protozoan) and chemicals (disinfection byproducts [DBPs]) were used as reference hazards. The exposure pathways for BAU included accidental ingestion of contaminated recreational water, ingestion of cross-connected sewage to drinking water, and shower exposures to DBPs. The alternative systems included ingestion of treated greywater from garden irrigation, toilet flushing, and crop consumption; and ingestion of treated rainwater while showering. The pathways with the highest health impact included the ingestion of cross-connected drinking water and ingestion of recreational water contaminated by septic seepage. These were also among the most uncertain when characterizing input parameters, particularly the scale of the cross-connection event, and the removal of pathogens during groundwater transport of septic seepage. A comparison of the health burdens indicated potential health benefits by switching from BAU to decentralized water and wastewater systems. [ABSTRACT FROM AUTHOR]

This study aimed to compare the inactivation rate and the mechanisms of pathogenic bacteria in three matrixes (sawdust, rice husk and charcoal) during the composting process. The inactivation rate was evaluated withEscherichia colistrain and the damaged parts and/or functions were evaluated with three different media. Normalized inactivation rate constant in three media and from three matrixes had no significant difference in each process (pure, 1 month and 2 months). The value in rice husk was relatively increased during 2 months but there was no significant difference. The inactivation rate constants of Tryptic Soy Agar (TSA) and Compact DryE. coli/Coliform in pure sawdust and rice husk were relatively lower than that of Desoxycholate Agar, but increased in 2 months. This indicated that damaging part was changed from outer membrane to enzymes and metabolisms during the 2-month composting process. In the case of charcoal, only the TSA value in a pure matrix was relatively lower than that of others, but it increased in 2 months. This indicated that damaging part was changed from outer membrane and enzyme to metabolisms during the composting process. Composting matrix and composting process did not significantly affect inactivation rate of pathogenic bacteria during the process but affected the damaging part of the bacteria. [ABSTRACT FROM AUTHOR]

Highlights: [•] Composting toilets can be an alternative to flush based sanitation. [•] Many different composting toilet designs are available. [•] Composting is affected by moisture content, temperature, carbon to nitrogen ratio. [•] There are many barriers to composting toilets. [•] Research is needed in science based design of composting toilets. [Copyright &y& Elsevier]

Abstract: Harvested rainwater systems and composting toilets are expected to be an important part of sustainable solutions in buildings. Yet, to this date, a model evaluating their economic and environmental impact has been missing. To address this need, a life cycle based model, EEAST was developed. EEAST was designed to compare the business as usual (BAU) case of using potable water for toilet flushing and irrigation to alternative scenarios of rainwater harvesting and composting toilet based technologies. In EEAST, building characteristics, occupancy, and precipitation are used to size the harvested rainwater and composting toilet systems. Then, life cycle costing and life cycle assessment methods are used to estimate cost, energy, and greenhouse gas (GHG) emission payback periods (PPs) for five alternative scenarios. The scenarios modeled include use of harvested rainwater for toilet flushing, for irrigation, or both; and use of composting toilets with or without harvested rainwater use for irrigation. A sample simulation using EEAST showed that for the office building modeled, the cost PPs were greater than energy PPs which in turn were greater than GHG emission PPs. This was primarily due to energy and emission intensive nature of the centralized water and wastewater infrastructure. The sample simulation also suggested that the composting toilets may have the best performance in all criteria. However, EEAST does not explicitly model solids management and as such may give composting toilets an unfair advantage compared to flush based toilets. EEAST results were found to be very sensitive to cost values used in the model. With the availability of EEAST, life cycle cost, energy, and GHG emissions can now be performed fairly easily by building designers and researchers. Future work is recommended to further improve EEAST and evaluate it for different types of buildings and climates so as to better understand when composting toilets and harvested rainwater systems outperform the BAU case in building design. [Copyright &y& Elsevier]

End-product from 16 public mixed latrine style composting toilets (CTs) at 12 sites between 50 and 2100 m.a.s.l. in Western North America was tested in order to evaluate the effect of composting variables (TS%, NH3–N, temperature, and material age) on compost quality and hygiene (VS%, Escherichia coli, –N, and pH). Principal component analysis indicated that TS%, temperature, and material age equally contributed to reduction in VS%. NH3–N had the greatest effect on –N, E. coli, and pH. Nitrification was significantly inhibited above 386 mg/kg NH3–N, but no such limit was found for E. coli, despite a significant (p = 0.016) but weak (r 2 = 0.11) negative relationship. It may be possible to amplify the sanitizing effect of ammonia and overcome pathogen resistance due to low temperatures and re-contamination (caused by poor design) with generous dosing of urea and ash. However, even sanitized, the fertilization effect of discharged material on the natural environment may not be desired or permitted in parks or protected areas where many CTs were found. To this end, operators of CTs need to evaluate their primary management objectives and ensure congruency with proven system capabilities. [Copyright &y& Elsevier]

The current sanitation technology in developed countries is based on diluting human excreta with large volumes of centrally provided potable water. This approach is a poor use of water resources and is also inefficient, expensive, and energy intensive. The goal of this study was to compare the standard sanitation technology (Scenario 1) with alternative technologies that require less or no potable water use in toilets. The alternative technologies considered were high efficiency toilets flushed with potable water (Scenario 2), standard toilets flushed with rainwater (Scenario 3), high efficiency toilets flushed with rainwater (Scenario 4), and composting toilets (Scenario 5). Cost, energy, and carbon implications of these five design scenarios were studied using two existing University of Toledo buildings. The results showed that alternative systems modeled in Scenarios 2, 4, and 5 were viable options both from an investment and an environmental performance perspective. High efficiency fixtures that use potable water (Scenario 2) is often the most preferred method in high efficiency buildings due to reduced water use and associated reductions in annual water and wastewater costs. However, the cost, energy, and CO2EE analyses all showed that Scenarios 4 and 5 were preferable over Scenario 2. Cost payback periods of scenarios 2, 4 and 5 were less than 10 years; in the future, increase in water and wastewater services would further decrease the payback periods. The centralized water and wastewater services have high carbon footprints; therefore if carbon footprint reduction is a primary goal of a building complex, alternative technologies that require less potable water and generate less wastewater can largely reduce the carbon footprint. High efficiency fixtures flushed with rainwater (Scenario 4) and composting toilets (Scenario 5) required considerably less energy than direct energy demands of buildings. However, the annual carbon footprint of these technologies was comparable to the annual carbon footprint from space heating. Similarly, the carbon savings that could be achieved from Scenario 4 or 5 were comparable to a recycling program that can be implemented in buildings. [Copyright &y& Elsevier]

The usual phrase is "buildings in nature," which raises in an orderly way the question of proper relationships between the built human environment and the much more complex and much, much larger natural environment in which it resides. This paper explores the less orderly, less comfortable, and riskier connections that arise when nature in one or another form comes directly into buildings. Distinguished built projects, such as Tezuka Architecture's Fuji Kindergarten, share the stage with humble services such as indoor beehives and composting toilets. The concept of biophilia confronts pest control. Neighborhood raccoons and friendly spiders give further clues as to what presence of nature in buildings could be welcome and achievable, and what value choices and feasibility puzzles design may have to unravel to get there. [ABSTRACT FROM AUTHOR]

This paper argues that "new" sustainable technologies being used to manage human waste--composting toilets, bioremediation, and biodigestion--are essentially reviving the medieval strategy of waste management: containment and reuse of waste, as opposed to the modern strategy of dilution and evacuation. This debate should not occur in a vacuum, uninformed by the motivations for, and history of, the development of the modern system. Therefore, this paper more closely examines the medieval system, which closely linked waste and agricultural production. It then considers the transformation to the modern system, using the design of Leonardo da Vinci's city of Romorantin as a case study. It is argued that this transformation was largely predicated on now-delegitimized miasmic theory, which held foul or corrupt air to be the cause of disease, and that it precipitated larger changes in the urban environment. In light of this historical view it is suggested that contemporary sustainable technologies imply larger changes in the form of human settlement, and that the nature of these changes must be explored further. [ABSTRACT FROM AUTHOR]

Engineering education has focused on the mathematical and scientific principles which underpin proper design. Technological capabilities have, in some instances, overcome society's ability to adapt behavior to new technologies. Sustainable systems should be engineered to address economic, environmental, and behavioral issues as well as technical issues. Developing education curricula that encourages students to consider all facets involved in sustainable systems has challenged engineering programs. A pilot course based upon the design of a sanitation facility for a school in Azové, Benin, was taught in the 2004–2005 academic year. The objective of the course was to create a meaningful project that would teach sustainability as part of the design process. Over 1,200 7th- to 10th-grade students at CEG in Azové lack access to clean water and basic sanitation facilities. A site visit to the CEG confirmed that water and sanitation were priorities of the school board and parents of the children. Students at Gonzaga University designed a water and sanitation system for CEG and learned about sustainability requirements for structures, hydraulics, and water and wastewater treatment. Upon implementation of the proposed design, exposure to pathogenic organisms is expected to decrease substantially. Students were encouraged to consider sustainability issues in design and problems associated with water and sanitation in the developing world. Incorporating sustainability lessons through design and peer presentation significantly improved the education in global awareness and sustainability as perceived by students and professionals. [ABSTRACT FROM AUTHOR]

Centralized waterborne sanitation faces serious social, economic and environmental sustainability challenges. Dry sanitation (DS) may ease some of those, but it is not known whether DS can be a viable solution at large scales and in urban settings. We assessed DS viability in a broad range of large scale and urban contexts in Mexico. Here, we synthesize the operational and structural barriers encountered across a diversity of sites, provide an understanding of how and why those barriers arose and propose a set of strategies through which those barriers can be addressed. We include reference to other large-scale and urban experiences outside Mexico. [ABSTRACT FROM AUTHOR]

Dry sanitation (DS) may be part of the solution to water scarcity, water quality deterioration and lack of resources to provide or maintain waterborne sewage systems. However, the worldwide paucity of large-scale, urban case studies makes assessment of DS as a potential urban water management strategy difficult. Urban DS viability depends in part on urban users' satisfaction with dry toilets (DTs) and whether they would accept them as long-term sanitation options. We analyze user acceptance and satisfaction with DS in five Mexican cities. When toilets functioned well (four out of five sites), users were highly satisfied. Similar levels of satisfaction were found under conditions of different DT models, types of DS program and income-level of the population. User motivation, choice and adequate support services were positively associated with satisfaction. Incentives such as indoor, aesthetic DTs, maintenance and end-product collection services, as well as higher water supply pricing, would encourage people to accept DS as a long-term option. We discuss reasons for dissatisfaction at one of the study sites. [ABSTRACT FROM AUTHOR]

Dry sanitation systems (waterless or composting toilets) have been used since the 1970s. Their use has received acceptance in rural regions of Europe and the United States. Some of the advantages of dry sanitation systems include their waterless nature, their low energy requirement and the creation of fertilizer as an added value product. Moreover, the use of such a system is a sustainable sanitation approach that may reduce the burden on infrastructure and provide sanitation to the 2.5 billion people worldwide who do not currently have access to it. The critical factors when choosing a dry sanitation system and their optimum parameters include aeration, moisture content (50%–60%), temperature (40–65 °C), carbon to nitrogen ratio (25–35), pH (5.5–8.0) and porosity (35%–50%). The temperature–time criterion approach is the most common method used to evaluate the stability and safety of the compost as a fertilizer. The risks of handling the waste after 12 months of composting have been calculated as low. Here, we have reviewed and assessed the features of dry sanitation systems currently available, focusing on those designed for and operated in remote areas such as national parks and tourist destinations and, more importantly, in rural areas in developing countries or refugee shelters where water/sanitation may be scarce. [ABSTRACT FROM AUTHOR]

Several letters to the editor are presented in response to articles in previous issues including an article related to the use of the term doctors by chartered engineers, another article related to the use of the term engineers by elite people by Ian Waite in the December 2012 issue and "Thinking outside the thunderbox" in the December 2012. INSET: ALL ENGINEERS DESERVE RESPECT.