Groundwater implications on methane emission from non-sewered sanitation systems in Nepal.

Non-sewered sanitation systems (NSSS) are identified as significant contributors of greenhouse gases (GHGs), primarily due to biological processes occurring within the containment systems. In unsealed or unlined containment systems like pit latrines, the emissions are influenced by moisture. This work quantified the GHG emission from unlined or unsealed containments prevalent in Nepal and compared it with sealed containment-like septic tanks, where the chances of groundwater (GW) inundation are low. The modeled GW data extracted from the secondary sources were validated with available national data. The emissions were quantified using the Intergovernmental Panel for Climate Change (IPCC) model for different ecological and provincial divisions of Nepal. Spatial representation for the results was done using the Geographical Information System (GIS) tool. The total methane (CH4) emission occurring from the various NSSS was determined to be 2618 Gg CO2 e per year which is almost twice the emission from the waste sector in 2011, as reported by the recent national communication submitted to the United Nations Framework Convention on Climate Change (UNFCC). Variation of the CH4 emission was found to be prominent in lowlands (Terai region) with total national emissions of 1329.37 Gg CO2e per year. The lowland has a shallow GW table that can easily inundate the unlined containments like pit latrines thus contributing to more anaerobic conditions which may lead to higher CH4 emissions compared to containments in mid and highlands. This study concludes that the GHG emissions occurring from NSSS are substantial and addressing these emissions can help fulfil the Nationally Determined Contributions (NDCs) in the waste sector.

Field-based methods for measuring greenhouse gases emissions from on-site sanitation systems: A systematic review of published literature.

On-site sanitation systems (OSS) are a source of greenhouse gas (GHG) emissions. Although efforts have been made recently to measure and quantify emissions from septic tanks using various field-based methods, the vast majority of published literature reporting GHG emissions from OSS units (e.g., pits and tanks) is based on non-empirical evidence. This systematic review presents an overview and limitations of field-based methods used for the quantification of GHG emissions from OSS. Papers published in English were searched in three databases: Google Scholar, PubMed, and Directory of Articles and Journals. Peer-reviewed papers that reported field-based methods applied to containment units in OSS were included in this study. Only eight out of 2085 papers met the inclusion criteria with septic tanks as the sole technology reported and were thus, considered for the review. Most of the studies have been conducted in middle- and high-income countries. Field-based measurements of GHGs are conducted using a flux chamber (FC) and the most commonly used FC methods are (a) the modified simple static FC, (b) automated static FC, and (c) floating FC. Data reported in published studies do not provide sufficient information on the calibration and validation of the results from the FCs used. The complex FC designs, laborious fieldwork operations, and reliance on expensive, specialist equipment, suggest that such methods may not be suitable in Low and Middle-Income countries (LMICs), where resources and access to laboratory facilities are limited. Also, the complexity of pits and tank typology in LMICs (i.e., unstandardised designs and sizes) may be a challenge to the use of FCs with fixed dimensions and set operational conditions. The variation in the quantification methods and resulting emission rates among the studies indicates that gaps prevail in the use of existing methods. Therefore, there is still a need for a simple field-based, easily adaptable FC method with adequate calibration and validation that can help in reliably quantifying the emissions from different OSS in any LMICs.

Algae-based treatment of a landfill leachate pretreated by coagulation-flocculation.

Landfill leachate (LL) management is an urgent issue at recently closed Sisdol Landfill Site (SLS) used to dispose of solid waste generated in Kathmandu (Nepal) as untreated leachate is flowing directly to the nearby Kolpu River causing environmental and health concerns. This study aims to assess the potential of algae-based treatment of LL pretreated by optimized coagulation-flocculation (CF) for the removal of conventional pollutants such as biological oxygen demand (BOD5), chemical oxygen demand (COD), ammonia, nitrate, and phosphate. Response Surface Methodology (RSM) was used to optimize the operating variables (dose and pH) during the pretreatment of leachate by the CF process using ferric chloride (FeCl3.7H2O), alum (Al2(SO4)3.6H2O) and commercial poly aluminium chloride (PAC) as coagulants using a jar test apparatus. The pretreated LL was subjected to algal treatment using the mixed microalgae culture isolated and enriched from the wastewater collection pond and grown in artificial light. The combined physicochemical and algal treatment of LL from SLS achieved 62.93-72.43%, 74.93-75.55% and 87.58-93.40% and 73.63-86.73% removal for COD, BOD5, ammonium-nitrogen and phosphate, respectively. Thus, this research has proven the feasibility of a combined physiochemical and algae-based treatment of LL and also offers an exciting alternative to current treatment practices for LL.

Biohythane production from food waste in a two-stage process: assessing the energy recovery potential.

ABSTRACTBiohythane (hydrogen + methane) production in a two stage dark fermentation (DF) and anaerobic digestion (AD) process from food waste (FW) has been studied. This paper investigated the effect of operation temperature, i.e. mesophilic (34 °C) and thermophilic (55 °C) , on biohythane yield and total energy recovery carried out at the initial culture pH 5.5 and pH 7, respectively for DF and AD batch tests. The mesophilic DF tests gave a higher hydrogen yield of 53.5 (±4) mL H2/g VS added compared to thermophilic DF tests, i.e. 37.6 (±1) mL H2/g VS added. However, higher methane yields, i.e. 307.5 (± 10) mL CH4/g VS, were obtained at thermophilic AD tests compared to mesophilic AD, i.e. 276.5 (±4.3) mL CH4/g VS. The total energy recovery from thermophilic DF + AD was higher (11.4 MJ/kg VS) than the mesophilic (10.4 MJ/kg VS) combined process. Interestingly, the analysis of kinetic parameters of mesophilic tests, determined from the Modified Gompertz equation, showed that mesophilic DF had faster H2 production kinetics, which can be attributed to a faster adaptation of the heat-shocked inoculum used in the tests to the incubation temperature. However, thermophilic AD tests exhibited faster kinetics for methane production.

Purple phototrophic bacteria for resource recovery: Challenges and opportunities.

Sustainable development is driving a rapid focus shift in the wastewater and organic waste treatment sectors, from a "removal and disposal" approach towards the recovery and reuse of water, energy and materials (e.g. carbon or nutrients). Purple phototrophic bacteria (PPB) are receiving increasing attention due to their capability of growing photoheterotrophically under anaerobic conditions. Using light as energy source, PPB can simultaneously assimilate carbon and nutrients at high efficiencies (with biomass yields close to unity (1 g CODbiomass·g CODremoved-1)), facilitating the maximum recovery of these resources as different value-added products. The effective use of infrared light enables selective PPB enrichment in non-sterile conditions, without competition with other phototrophs such as microalgae if ultraviolet-visible wavelengths are filtered. This review reunites results systematically gathered from over 177 scientific articles, aiming at producing generalized conclusions. The most critical aspects of PPB-based production and valorisation processes are addressed, including: (i) the identification of the main challenges and potentials of different growth strategies, (ii) a critical analysis of the production of value-added compounds, (iii) a comparison of the different value-added products, (iv) insights into the general challenges and opportunities and (v) recommendations for future research and development towards practical implementation. To date, most of the work has not been executed under real-life conditions, relevant for full-scale application. With the savings in wastewater discharge due to removal of organics, nitrogen and phosphorus as an important economic driver, priorities must go to using PPB-enriched cultures and real waste matrices. The costs associated with artificial illumination, followed by centrifugal harvesting/dewatering and drying, are estimated to be 1.9, 0.3-2.2 and 0.1-0.3 $·kgdry biomass-1. At present, these costs are likely to exceed revenues. Future research efforts must be carried out outdoors, using sunlight as energy source. The growth of bulk biomass on relatively clean wastewater streams (e.g. from food processing) and its utilization as a protein-rich feed (e.g. to replace fishmeal, 1.5-2.0 $·kg-1) appears as a promising valorisation route.

Enhanced micropollutant biodegradation and assessment of nitrous oxide concentration reduction in wastewater treated by acclimatized sludge bioaugmentation.

This research investigated the micropollutant biodegradation and nitrous oxide (N2O) concentration reduction in high strength wastewater treated by two-stage activated sludge (AS) systems with (bioaugmented) and without (non-bioaugmented) acclimatized sludge bioaugmentation. The bioaugmented and non-bioaugmented systems were operated in parallel for 228 days, with three levels of concentrations of organics, nitrogen, and micropollutants in the influent: conditions 1 (low), 2 (moderate), and 3 (high). The results showed that, under condition 1, both systems efficiently removed the organic and nitrogen compounds. However, the bioaugmented system was more effective in the micropollutant biodegradation and N2O concentration reduction than the non-bioaugmented one. Under condition 2, the nitrogen and micropollutant biodegradation efficiency of the non-bioaugmented system slightly decreased, while the N2O concentration declined in the bioaugmented system. Under condition 3, the treatment performance and N2O concentration abatement were substantially lowered as the compounds concentration increased. Further analysis also showed that the acclimatized sludge bioaugmentation increased the bacterial diversity in the system. In essence, the acclimatized sludge bioaugmentation strategy was highly effective for the influent with low compounds concentration, achieving the organics and nitrogen removal efficiencies of 92-97%, relative to 71-97% of the non-bioaugmented system. The micropollutant treatment efficiency of the bioaugmented system under condition 1 was 75-92%, indicating significant improvement in the treatment performance (p < 0.05), compared with 60-79% of the non-bioaugmented system.

Effect of total solids content on biohydrogen production and lactic acid accumulation during dark fermentation of organic waste biomass.

Production of biohydrogen and related metabolic by-products was investigated in Solid State Dark Fermentation (SSDF) of food waste (FW) and wheat straw (WS). The effect of the total solids (TS) content and H2 partial pressure (ppH2), two of the main operating factors of SSDF, were investigated. Batch tests with FW at 10, 15, 20, 25 and 30% TS showed considerable effects of the TS on metabolites distribution. H2 production was strongly inhibited for TS contents higher than 15% with a concomitant accumulation of lactic acid and a decrease in substrate conversion. Varying the ppH2 had no significant effect on the conversion products and overall degradation of FW and WS, suggesting that ppH2 was not the main limiting factor in SSDF. This study showed that the conversion of complex substrates by SSDF depends on the substrate type and is limited by the TS content.

Bio-hythane production from microalgae biomass: Key challenges and potential opportunities for algal bio-refineries.

The interest in microalgae for wastewater treatment and liquid bio-fuels production (i.e. biodiesel and bioethanol) is steadily increasing due to the energy demand of the ultra-modern technological world. The associated biomass and by-product residues generated from these processes can be utilized as a feedstock in anaerobic fermentation for the production of gaseous bio-fuels. In this context, dark fermentation coupled with anaerobic digestion can be a potential technology for the production of hydrogen and methane from these residual algal biomasses. The mixture of these gaseous bio-fuels, known as hythane, has superior characteristics and is increasingly regarded as an alternative to fossil fuels. This review provides the current developments achieved in the conversion of algal biomass to bio-hythane (H2+CH4).

Photofermentative production of hydrogen and poly-ß-hydroxybutyrate from dark fermentation products.

The aim of this work is to investigate the hydrogen and poly-ß-hydroxybutyrate (PHB) production during the photofermentative treatment of the effluent from a dark fermentation reactor fed with the organic fraction of municipal solid waste. Two different inocula, an adapted culture of Rhodobacter sphaeroides AV1b and a mixed consortium of purple non sulphur bacteria have been investigated under the same operational conditions. Different hydrogen productivities of 364 and 559NmL H2 L-1 were observed for the Rhodobacter sphaeroides and the mixed culture consortium tests, respectively: the consortium of PNSB resulted 1.5-fold more productive than the pure culture. On the other hand, Rhodobacter sphaeroides culture showed a higher PHB productivity (155mg PHB g COD-1) than the mixed culture (55mg PHB g COD-1). In all the tests, the concomitant H2 and PHB production was associated to a dissolved COD removal higher than 80%.

Recent insights into the cell immobilization technology applied for dark fermentative hydrogen production.

The contribution and insights of the immobilization technology in the recent years with regards to the generation of (bio)hydrogen via dark fermentation have been reviewed. The types of immobilization practices, such as entrapment, encapsulation and adsorption, are discussed. Materials and carriers used for cell immobilization are also comprehensively surveyed. New development of nano-based immobilization and nano-materials has been highlighted pertaining to the specific subject of this review. The microorganisms and the type of carbon sources applied in the dark hydrogen fermentation are also discussed and summarized. In addition, the essential components of process operation and reactor configuration using immobilized microbial cultures in the design of varieties of bioreactors (such as fixed bed reactor, CSTR and UASB) are spotlighted. Finally, suggestions and future directions of this field are provided to assist the development of efficient, economical and sustainable hydrogen production technologies.

Concomitant biohydrogen and poly-ß-hydroxybutyrate production from dark fermentation effluents by adapted Rhodobacter sphaeroides and mixed photofermentative cultures.

This work aimed at investigating concomitant production of biohydrogen and poly-ß-hydroxybutyrate (PHB) by photofermentation (PF) using dark fermentation effluents (DFE). An adapted culture of Rhodobacter sphaeroides AV1b (pH 6.5, 24±2°C) achieved H2 and PHB yields of 256 (±2) NmLH2/g Chemical Oxygen Demand (COD) and 273.8mgPHB/gCOD (32.5±3% of the dry cells weight (DCW)), respectively. When a diluted (1:2) DFE medium was applied to the adapted pure and mixed photofermentative culture, the respective H2 yields were 164.0 (±12) and 71.3 (±6) NmLH2/gCOD and the PHB yields were 212.1 (±105.2) and 50.7 (±2.7) mgPHB/gCOD added, corresponding to 24 (±0.7) and 6.3 (±0) % DCW, respectively. The concomitant H2 and PHB production from the PF process gave a good DFE post treatment achieving up to 80% COD removal from the initial DFE.

Effects of operational parameters on dark fermentative hydrogen production from biodegradable complex waste biomass.

This work aimed to investigate the effect of the initial pH, combination of food to microorganism ratio (F/M) and initial pH, substrate pre-treatment and different inoculum sources on the dark fermentative biohydrogen (H2) yields. Three model complex waste biomasses (food waste, olive mill wastewater (OMWW) and rice straw) were used to assess the effect of the aforementioned parameters. The effect of the initial pH between 4.5 and 7.0 was investigated in batch tests carried out with food waste. The highest H2 yields were shown at initial pH 4.5 (60.6 ± 9.0 mL H2/g VS) and pH 5.0 (50.7 ± 0.8 mL H2/g VS). Furthermore, tests carried out with F/M ratios of 0.5, 1.0 and 1.5 at initial pH 5.0 and 6.5 revealed that a lower F/M ratio (0.5 and 1.0) favored the H2 production at an initial pH 5.0 compared to pH 6.5. Alkaline pre-treatment of raw rice straw using 4% and 8% NaOH at 55°C for 24h, increased the H2 yield by 26 and 57-fold, respectively. In the dark fermentation of OMWW, the H2 yield was doubled when heat-shock pre-treated activated sludge was used as inoculum in comparison to anaerobic sludge. Overall, this study shows that the application of different operating parameters to maximize the H2 yields strongly depends on the biodegradability of the substrate.

Dark fermentation of complex waste biomass for biohydrogen production by pretreated thermophilic anaerobic digestate.

The Biohydrogen Potential (BHP) of six different types of waste biomass typical for the Campania Region (Italy) was investigated. Anaerobic sludge pre-treated with the specific methanogenic inhibitor sodium 2-bromoethanesulfonic acid (BESA) was used as seed inoculum. The BESA pre-treatment yielded the highest BHP in BHP tests carried out with pre-treated anaerobic sludge using potato and pumpkin waste as the substrates, in comparison with aeration or heat shock pre-treatment. The BHP tests carried out with different complex waste biomass showed average BHP values in a decreasing order from potato and pumpkin wastes (171.1 ± 7.3 ml H2/g VS) to buffalo manure (135.6 ± 4.1 ml H2/g VS), dried blood (slaughter house waste, 87.6 ± 4.1 ml H2/g VS), fennel waste (58.1 ± 29.8 ml H2/g VS), olive pomace (54.9 ± 5.4 ml H2/g VS) and olive mill wastewater (46.0 ± 15.6 ml H2/g VS). The digestate was analyzed for major soluble metabolites to elucidate the different biochemical pathways in the BHP tests. These showed the H2 was produced via mixed type fermentation pathways.