BackgroundAn estimated 2.4 billion people still lack access to improved sanitation and 946 million still practice open defecation. The World Health Organization (WHO) commissioned this review to assess the impact of sanitation on coverage and use, as part of its effort to develop a set of guidelines on sanitation and health.Methods and findingsWe systematically reviewed the literature and used meta-analysis to quantitatively characterize how different sanitation interventions impact latrine coverage and use. We also assessed both qualitative and quantitative studies to understand how different structural and design characteristics of sanitation are associated with individual latrine use. A total of 64 studies met our eligibility criteria. Of 27 intervention studies that reported on household latrine coverage and provided a point estimate with confidence interval, the average increase in coverage was 14% (95% CI: 10%, 19%). The intervention types with the largest absolute increases in coverage included the Indian government's “Total Sanitation Campaign” (27%; 95% CI: 14%, 39%), latrine subsidy/provision interventions (16%; 95% CI: 8%, 24%), latrine subsidy/provision interventions that also incorporated education components (17%; 95% CI: −5%, 38%), sewerage interventions (14%; 95% CI: 1%, 28%), sanitation education interventions (14%; 95% CI: 3%, 26%), and community-led total sanitation interventions (12%; 95% CI: −2%, 27%). Of 10 intervention studies that reported on household latrine use, the average increase was 13% (95% CI: 4%, 21%). The sanitation interventions and contexts in which they were implemented varied, leading to high heterogeneity across studies. We found 24 studies that examined the association between structural and design characteristics of sanitation facilities and facility use. These studies reported that better maintenance, accessibility, privacy, facility type, cleanliness, newer latrines, and better hygiene access were all frequently associated with higher use, whereas poorer sanitation conditions were associated with lower use.ConclusionsOur results indicate that most sanitation interventions only had a modest impact on increasing latrine coverage and use. A further understanding of how different sanitation characteristics and sanitation interventions impact coverage and use is essential in order to more effectively attain sanitation access for all, eliminate open defecation, and ultimately improve health.

The City of Baltimore, Maryland evaluated the feasibility of converting the conventional high rate (CHR) anaerobic digesters to the two-phase (acid-gas) mesophilic anaerobic digestion process (two-phase process) at its 180-million-gallon per day (MGD) Back River Wastewater Treatment Plant (WWTP) using a dedicated 25-dry ton per day (dtpd) process evaluation facility (PEF). The evaluation of the two-phase process was performed in conjunction with an extensive upgrade of the digestion facilities. The PEF's acid phase reactor (APR) consisted of a new 200,000-gallon, tall, cylindrical vessel, the configuration of which was designed by the City. The gas, or methane, phase reactors (MPR), consisted of two existing 1.3-million gallon (MG), cylindrical, "flat," digesters. This paper provides the findings of the first 14 months of the evaluation during which time the two-phase and CHR processes were fed the same blend of thickened primary sludge (PS) and waste activated sludge (WAS). The CHR process was carried out in the plant's two existing three-MG egg-shaped digesters (ESDs).It was demonstrated that two-phase process operating conditions had been established in the PEF based on profiles through the system of the volatile fatty acid (VFA) concentration and the pH, and also by the headspace gas composition in the APR all being in agreement with two-phase process theory. Also, the VFA species composition of the APR effluent was comparable to the composition at two other municipal wastewater treatment plants using the two-phase process.At an APR solids loading rate (SLR) of 2.0 pounds of volatile solids per cubic foot per day (lbs VS/cf/day) of sludge averaging six percent solids concentration, the volatile solids destruction (VSD) performance of the two-phase process averaged 58 percent whereas it averaged 48 percent in the CHR process, as calculated by the mass-balance (MB) method. The solids retention time (SRT) in the two-phase process averaged 11-days. In terms of the thickened sludge volume fed to the digesters, digester gas (DG) production in the two-phase process averaged 3.92 cf/gal, whereas it averaged 2.99 cf/gal in the CHR process, at the SLR of 2.0 lbs VS/cf/day. At APR SLRs of 2.5 and 3.25 lbs VS/cf/day, the VSD performance of the two-phase process was not improved relative to the CHR process. The DG production as a function of VSD was nearly equal in the two-phase and CHR processes, ranging from 15 to 17 cf/lb VS destroyed.The APR was operated mesophilically in an upflow mode at a recirculation ratio of about 7.5:1, with a heated mixture of raw and recirculated APR sludge introduced to the bottom of the reactor and with the effluent being withdrawn from the top. Lithium chloride tracer tests in the APR demonstrated the flow regime approximated that of a complete mix reactor rather than a plug flow reactor. While tracer tests were not performed in the MPRs, based on the City's operating and maintenance experience, it appears that the MPRs also operated in a complete mix flow regime with hydraulic short-circu...

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