Inactivation of viable Ascaris eggs during faecal sludge co-composting with chicken feathers and market waste

Faecal Sludge (FS) contains high concentrations of pathogenic microorganisms that are 10–100 times higher than those in domestic wastewater. Proper and sustainable treatment is required to inactivate these pathogens if FS is to be recycled in agriculture, so as to minimise public health and environmental risks. Composting is one of the common low-cost technologies of sanitising FS in Urban Africa; however, it is associated with longer pathogen inactivation periods that make it commercially uneconomical. This study investigated the effect of different organic wastes types and their mixing ratios with FS on the inactivation efficiency of viable Ascaris eggs (suum and lumbricoides) during composting. Dewatered FS was mixed with market waste (MW), chicken feathers (CF) and sawdust (SD) in different ratios. Compost piles of FS:MW:SD and FS:CF:SD both in volumetric ratios of 1:2:1 and 1:3:1 were set-up in duplicate (3m3 each), composted and monitored weekly for viable Ascaris eggs presence for a period of 15 weeks. The results suggest that the organic waste types have a significant effect on the temperature evolution and pathogen inactivation efficiency while their mixing ratios do not. Piles containing CF achieved the shortest pathogen survival period of 4 weeks compared with 6–8 weeks for those with MW. The temperature–time factor was found to be the most important variable responsible for viable Ascaris eggs inactivation. However, other mechanisms such as microbial antagonism or antibiotic action induced by indigenous microorganisms and toxic by-products such as free ammonia were found to have also played an important role in Ascaris eggs inactivation. All piles attained 100% Ascaris eggs inactivation from FS, and therefore, the compost was safe for use in agriculture. The study findings suggest that composting of FS with CF can reduce Ascaris eggs inactivation periods by 42%, which may thus reduce the operational costs of FS treatment facilities

Nitrification-denitrification in WSP: a mechanism for permanent nitrogen removal in maturation ponds

A pilot-scale primary maturation pond was spiked with 15N-labelled ammonia (15NH4Cl) and 15N labelled nitrite (Na15NO2), in order to improve current understanding of the dynamics of inorganic nitrogen transformations and removal in WSP systems. Stable isotope analysis of δ15N showed that nitrification could be considered as an intermediate step in WSP, which is masked by simultaneous denitrification, under conditions of low algal activity. Molecular microbiology analysis showed that denitrification can be considered a feasible mechanism for permanent nitrogen removal in WSP, which may be supported either by ammonia-oxidising bacteria (AOB) or by methanotrophs, in addition to nitrite-oxidising bacteria (NOB). However, the relative supremacy of the denitrification process over other nitrogen removal mechanisms (e.g., biological uptake) depends upon phytoplanktonic activity

Hydrogen via reforming aqueous ammonia and biomethane co-products of wastewater treatment: environmental and economic sustainability

Green H2 is increasingly viewed as a key energy carrier for the fight against climate change. Wastewater treatment plants (WWTPs) have the unique potential to be centres of renewable H2 generation with the growing availability of two attractive feedstocks: biomethane and ammonia. An innovative and novel method of ammonia recovery from digestate liquor followed by a state-of-the-art H2 production process named NWaste2H2 is demonstrated for a case-study WWTP. The recovered ammonia is used alongside biomethane for H2 production and its diversion from conventional biological treatment has two other crucial benefits, with reductions in both associated electricity demand and emissions of nitrous oxide, an extremely potent greenhouse gas. Process modelling, supported by extensive experiments in a packed-bed reactor at bench-scale, demonstrate the prized capability of simultaneously performing steam methane reforming and ammonia decomposition to generate a H2-rich syngas with yields close to equilibrium values. Greenhouse gas emission abatement from the replacement of diesel buses and reduced N2O emissions from biological treatment could save up to 17.2 kg CO2 equivalent (CO2e) per year for each person served by the WWTP. An in-depth economic study illustrates the ability to achieve a positive net present value with a 10% discount factor as early as 5.8 years when the H2 is prepared and sold to power fuel cell electric buses

An Effective Surrogate Tracer Technique for S. aureus Bioaerosols in a Mechanically Ventilated Hospital Room Replica Using Dilute Aqueous Lithium Chloride

Finding a non-pathogenic surrogate aerosol that represents the deposition of typical bioaerosols in healthcare settings is beneficial from the perspective of hospital facility testing, general infection control and outbreak analysis. This study considers aerosolization of dilute aqueous lithium chloride (LiCl) and sodium chloride (NaCl) solutions as surrogate tracers capable of representing Staphylococcus aureus bioaerosol deposition on surfaces in mechanically ventilated rooms. Tests were conducted in a biological test chamber set up as a replica hospital single patient room. Petri dishes on surfaces were used to collect the Li, Na and S. aureus aerosols separately after release. Biological samples were analyzed using cultivation techniques on solid media, and flame atomic absorption spectroscopy was used to measure Li and Na atom concentrations. Spatial deposition distribution of Li tracer correlated well with S. aureus aerosols (96% of pairs within a 95% confidence interval). In the patient hospital room replica, results show that the most contaminated areas were on surfaces 2 m away from the source. This indicates that the room’s airflow patterns play a significant role in bioaerosol transport. NaCl proved not to be sensitive to spatial deposition patterns. LiCl as a surrogate tracer for bioaerosol deposition was most reliable as it was robust to outliers, sensitive to spatial heterogeneity and found to require less replicates than the S. aureus counterpart to be in good spatial agreement with biological results

Enhancing bioenergy production from food waste by in situ biomethanation: Effect of the hydrogen injection point

The increasing rate of food waste (FW) generation around the world is a growing environmental concern, notwithstanding, its valorisation through anaerobic digestion (AD) makes it a potential resource. Moreover, there is a growing demand to optimise the biomethane from AD for gas‐to‐grid (GtG) and vehicular applications. This has spurred researches on hydrogen gas (H2) injection into AD systems to enhance the biological conversion of H2 and carbon dioxide (CO2) to methane (CH4), a process known as biomethanation. A simplistic approach for biomethanation is to add H2 directly into working AD reactors (in situ biomethanation). However, a competition for the injected H2 towards other biological reactions besides H2/CO2 conversion to CH4 could follow, thus, reducing the efficiency of the system. Hence, this study was conducted to understand how different H2 injection points would affect H2/CO2 conversion to CH4 during FW in situ biomethanation, to identify an optimal injection point. Experiments were designed using H2 equivalent to 5% of the head‐space of the AD reactor at three injection points representing different stages of AD: before volatile fatty acids (VFA) accumulation, during VFA accumulation and at depleted VFA intermediates. Lower potential for competitive H2 consumption before the accumulation of VFA enabled a high H2/CO2 conversion to CH4. However, enhanced competition for soluble substrates during VFA accumulation reduced the efficiency of H2/CO2 conversion to CH4 when H2 was added at this stage. In general, 12%, 4% and 10% CH4 increases as well as 39%, 25% and 34% CO2 removal were obtained for H2 added before VFA accumulation, during VFA accumulation and at depleted VFA intermediates, respectively. For immediate integration of biomethanation with existing AD facilities, it is suggested that the required H2 be obtained biologically by dark fermentation

Recycling of Faecal Sludge: Nitrogen, Carbon and Organic Matter Transformation during Co-Composting of Faecal Sludge with Different Bulking Agents

This study investigated the effect of locally available bulking agents on the faecal sludge (FS) composting process and quality of the final FS compost. Dewatered FS was mixed with sawdust, coffee husk and brewery waste, and composted on a pilot scale. The evolution of physical and chemical characteristics of the composting materials was monitored weekly. Results indicate that bulking agents have a statistically significant effect (p < 0.0001) on the evolution of composting temperatures, pH, electrical conductivity, nitrogen forms, organic matter mineralisation, total organic carbon, maturity indices, quality of the final compost and composting periods during FS composting. Our results suggest reliable maturity indices for mature and stable FS compost. From the resource recovery perspective, this study suggests sawdust as a suitable bulking agent for co-composting with FS—as it significantly reduced the organic matter losses and nitrogen losses (to 2.2%), and improved the plant growth index, thus improving the agronomic values of the final compost as a soil conditioner. FS co-composting can be considered a sustainable and decentralised treatment option for FS and other organic wastes in the rural and peri-urban communities, especially, where there is a strong practice of reusing organic waste in agriculture

Modelling Mechanically Induced non-Newtonian Flows to Improve the Energy Efficiency of Anaerobic Digesters

In this paper, a finite volume based computational fluid dynamics (CFD) model has been developed for investigating the mixing of non-Newtonian flows and operating conditions of an anaerobic digester. A CFD model using the multiple reference frame has been implemented in order to model the mixing in an anaerobic digester. Two different agitator designs have been implemented: a design currently used in a full-scale anaerobic mixing device, SCABA, and an alternative helical ribbon design. Lab-scale experiments have been conducted with these two mixing device designs using a water-glycerol mixture to replicate a slurry with total solids concentration of 7.5%, which have been used to validate the CFD model. The CFD model has then been scaled up in order to replicate a full-scale anaerobic digester under real operating parameters that is mechanically stirred with the SCABA design. The influence of the non-Newtonian behaviour has been investigated and found to be important for the power demand calculation. Furthermore, the other helical mixing device has been implemented at full scale and a case study comparing the two agitators has been performed; assessing the mixing capabilities and power consumption of the two designs. It was found that, for a total solids concentrations of 7.5%, the helical design could produce similar mixing capabilities as the SCABA design at a lower power consumption. Finally, the potential power savings of the more energy efficient helical design has been estimated if implemented across the whole of the United Kingdom (UK)/Austria

Towards sustainable sanitation management: Establishing the costs and willingness to pay for emptying and transporting sludge in rural districts with high rates of access to latrines

MOTIVATION: Proper management of fecal sludge has significant positive health and environmental externalities. Most research on managing onsite sanitation so far either simulates the costs of, or the welfare effects from, managing sludge in situ in pit latrines. Thus, designing management strategies for onsite rural sanitation is challenging, because the actual costs of transporting sludge for treatment, and sources for financing these transport costs, are not well understood. METHODS: In this paper we calculate the actual cost of sludge management from onsite latrines, and identify the contributions that latrine owners are willing to make to finance the costs. A spreadsheet-based model is used to identify a cost-effective transport option, and to calculate the cost per household. Then a double-bound contingent valuation method is used to elicit from pit-latrine owners their willingness-to-pay to have sludge transported away. This methodology is employed for the case of a rural subdistrict in Bangladesh called Bhaluka, a unit of administration at which sludge management services are being piloted by the Government of Bangladesh. RESULTS: The typical sludge accumulation rate in Bhaluka is calculated at 0.11 liters/person/day and a typical latrine will need to be emptied approximately once every 3 to 4 years. The costs of emptying and transport are high; approximately USD 13 per emptying event (circa 14% of average monthly income); household contributions could cover around 47% of this cost. However, if costs were spread over time, the service would cost USD 4 per year per household, or USD 0.31 per month per household-comparable to current expenditures of rural households on telecommunications. CONCLUSION: This is one of few research papers that brings the costs of waste management together with financing of that cost, to provide evidence for an implementable solution. This framework can be used to identify cost effective sludge management options and private contributions towards that cost in other (context-specific) administrative areas where onsite sanitation is widespread

Performance of Anaerobic Baffled Reactor for Decentralized Wastewater Treatment in Urban Malang, Indonesia

In order to assess the impact of the Sanitation by Communities (SANIMAS) program for community-led sanitation in Indonesia (established in 2002), this research work was conducted with the aim of characterizing the current performance of anaerobic baffled reactors (ABRs), which were deployed in high numbers for the provision of domestic wastewater treatment in densely populated urban areas in Malang (Indonesia). Small and decentralized sewage treatment facilities serve ⇡3% of the total population in Malang, including 89 ABR treatment plants. Our findings reveal that only 14% of the 89 ABRs in Malang have an acceptable performance with regard to pollutant removal and integrity of their building structure, but the majority of them produce a treated effluent of poor quality, according to discharge consents set by the Ministry of Environment and Forestry of the Republic of Indonesia (Regulation No. P.68/2016). Clearly the lack of consistent operation and maintenance practices have had a detrimental effect on these decentralized sewage treatment systems, despite their robustness and buffer capacity to cope with changes in organic and hydraulic loading rates. Urbanization will continue to exert pressure on the provision of sanitation services in lower and middle economies, and the role of decentralized sewage management systems is expected to be prominent in the UN’s Sustainable Development Goals era (2015–2030); however, sustainable service delivery must be conceived beyond the provision of sanitation infrastructure

Towards resolving the phosphorus chaos created by food systems

© 2019, The Author(s). The chaotic distribution and dispersal of phosphorus (P) used in food systems (defined here as disorderly disruptions to the P cycle) is harming our environment beyond acceptable limits. An analysis of P stores and flows across Europe in 2005 showed that high fertiliser P inputs relative to productive outputs was driving low system P efficiency (38 % overall). Regional P imbalance (P surplus) and system P losses were highly correlated to total system P inputs and animal densities, causing unnecessary P accumulation in soils and rivers. Reducing regional P surpluses to zero increased system P efficiency (+ 16 %) and decreased total P losses by 35 %, but required a reduction in system P inputs of ca. 40 %, largely as fertiliser. We discuss transdisciplinary and transformative solutions that tackle the P chaos by collective stakeholder actions across the entire food value chain. Lowering system P demand and better regional governance of P resources appear necessary for more efficient and sustainable food systems