More than 80 per cent of wastewater from human activities is discharged into the rivers or sea without any pollution removal, and the Sustainable Development Goals (SDGs) aim to halve this proportion and increase recycling and reuse globally by 2030. Treatment plants in Sub-Saharan Africa often fail due to lack of operating funds, poor regulation and poor design that does not take into account human factors. The failure of treatment plants can also be put down partly to the funding structures for management, which are often dependent on the disposal tariffs charged. Without sufficient regulation and enforcement, which is often lacking in Sub-Saharan Africa, this often leads to illegal disposal of faecal sludge. Due to the nutrient content and energy potential of wastewater, there is increasing focus on reuse of faecal sludge in ways that can contribute funds for maintenance and incentivise good management of treatment facilities. This research investigates potential designs for the re-use of faecal sludge in small cities in Sub-Saharan Africa to ensure proper treatment. Conducting two case studies using qualitative and quantitative methods, the research looks at the potential for re-use to be scaled up in Sunyani, Ghana and Mzuzu, Malawi, and whether different designs can ensure good management. Building upon the research investigation into how previous designs have failed in case studies, the research also investigates the use of agent-based modelling (ABM) as a modelling approach to explore social and technical aspects of sanitation systems to predict how different designs and management approaches can work. In Sunyani, biogas was the most acceptable option to customers whilst also providing a good business model to fund faecal sludge treatment, either as a decentralised system at public toilets where the fresh sludge is better for biogas production, or centrally at the existing disposal site. The success of biogas as a model that can fund maintenance and ensure good management would depend on the faecal sludge quality of public toilet sludge in the city and the investment level required and how any operating approach would work between the government and private sector. In Mzuzu, two main approaches to faecal sludge re-use exist currently: the implementation of Skyloos as above ground household toilets which provide compost, and a central disposal site from which compost is illegally harvested. At disposal, farmers remove sludge from the ponds and apply it untreated directly onto agricultural land. At times, private sector emptying services do not use the ponds, but also apply untreated sludge to agricultural land. Skyloos were found to have varying levels of success from different Non- Governmental Organisation (NGO) projects, with key sustainability issues being the availability of financing mechanisms, management between landlords and tenants and the trust of and engagement with implementing organisations. Existing approaches to waste management and re-use were found to be inaccessible and not working when implemented for the poorest and people with disabilities. Adopting re-use of faecal sludge in agriculture in Malawi would require improved marketing of sanitation options, financing options for households to incentivize adopting the technology, not targeting to poorest households and people with disabilities, and an improved management model for the treatment site to ensure safe disposal and production of compost. Looking at ABM as a way of modelling faecal sludge treatment systems in Sub- Saharan Africa, two models of different approaches in Mzuzu were developed to look at scaling up Skyloo toilets and managing the treatment plant. Both models demonstrate the potential of ABM to incorporate social and technical aspects into predicting the performance of different designs and approaches. The success and use of modelling depends on the quality of data that can be collected before implementing system approaches. Overall the thesis presents different models of treatment and re-use that can work and contribute to operating and maintenance of systems. It is unlikely that any design system will be so profitable that the treatment and re-use of sludge will be able to ensure good management without regulation, so the success of designs depends on relationships between the government and private sector and households in small cities.

No description available.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Steven K. Dentel and Pei C. Chiu, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (M. Sc.)(Microbiology)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references. Available on the Internet via the World Wide Web.

El consum energètic representa un 30 % dels costos d'operació en sistemes intensius de tractament d'aigües residuals urbanes. En depuradores convencionals que utilitzin un sistema de fangs activats, entorn al 15-20 % de l'energia és consumida en la línia dels fangs, que inclou el bombeig, l'espessiment, l'estabilització i la deshidratació. Per tant, la optimització de la gestió dels fangs pot contribuir substancialment en la reducció dels costos de tractament d'aigües residuals. La digestió anaeròbia termofílica és més eficient que la mesofílica i pscicrofílica, en termes de producció de biogàs i metà, eliminació de sòlids volàtils (SV) i destrucció de patògens. El procés es pot accelerar mitjançant el pre¬tractament dels fangs, afavorint la seva solubilització i hidròlisi. L'objecte d'aquesta Tesi Doctoral fou estudiar l'impacte dels paràmetres del procés en la digestió anaeròbia termofílica dels fangs de depuradora urbana, avaluar l'efecte del pre-tractament tèrmic dels fangs a baixa temperatura, i valorar processos alternatius des del punt de vista energètic. Els resultats experimentals presentats s'obtingueren mitjançant l'operació de dos reactors de laboratori durant prop de dos anys. En aquest període es va estudiar l'efecte de la temperatura del procés, del temps de retenció dels fangs (TRF), de la velocitat de càrrega orgànica (VCO) i del pre-tractament a 70 ºC en la digestió anaeròbia dels fangs de depuradora. El procés fou avaluat en termes de la producció d'energia (biogàs i metà) i de la qualitat del fang digerit (contingut de SV i d'àcids grassos volàtils (AGV), facilitat de deshidratació i higienització). S'analitzà l'estabilitat del procés a mesura que es reduïa el TRF i s'incrementava la VCO, i es comparà l'eficiència en períodes d'estabilitat corresponents a les diferents condicions operacionals. Finalment, s'avaluaren els resultats des del punt de vista energètic, mitjançant el càlcul de balanços i ratis energètics teòrics, que es compararen amb els resultats obtinguts a partir de dades experimentals d'altres estudis. També s'utilitzà un model cinètic de primer ordre. Les conclusions que es desprenen d'aquest treball es resumeixen a continuació: Durant la digestió anaeròbia dels fangs, la transició d'un reactor mesophilic (43 ºC) a termofílic (50 ºC) es podria dur a terme sense alterar el procés, treballant a TRF elevats (≥ 30 dies) i VCO baixes (≤ 0.5 kg SV m-3reactor d-1). En aquestes condicions, les principals diferències entre reactors termofílics (50-55 ºC) i mesofílics (38-43 ºC) fan referència a una certa acumulació d'AGV (0.5-2.5 g L-1) i millora de la destrucció de patògens (E. coli ≤ 102 UFC mL-1). La digestió termofílica a 50 ºC i 55 ºC dóna lloc a resultats similars pel que fa a la producció de biogàs, estabilització, higienització i facilitat de deshidratació de l'efluent, si no varien els altres paràmetres operacionals. La producció de metà tendeix a incrementar proporcionalment a la VCO, és a dir al TRF i el contingut de SV als fangs alimentats. Així mateix, la qualitat de l'efluent (contingut de SV i AGV, facilitat de deshidratació dels fangs) també depèn de la VCO. D'acord amb els resultats obtinguts a 55 ºC, la producció de metà s'incrementà 2-3 vegades (de 0.2 a 0.4-0.6 m3CH4 m3reactor d-1) en disminuir el TRF de 30 a 15-10 dies, incrementant la VCO de 0.5 a 2.5-3.5 kg SV m3reactor d-1. En canvi, el procés es desestabilitzà amb la reducció del TRF a 6 dies i VCO per sobre de 5 kg SV m3reactor d-1. Les següents concentracions poden ser útils per detectar i prevenir la desestabilització d'un digestor termofílic de fangs: AGV totals (2.5 g L-1), acetat (0.5 g L-1), rati acetat/propionat (0.5), alcalinitat intermèdia (1.8 g CaCO3 L-1), rati alcalinitat intermèdia/alcalinitat parcial (0.9), rati alcalinitat intermèdia/alcalinitat total (0.5), contingut de metà al biogàs (55 %). El pre-tractament a 70 ºC afavoreix la solubilització dels fangs, incrementant la proporció de matèria orgànica soluble respecte la matèria orgànica total del 5 % al 50 % en 9-24 h; seguit d'una progressiva generació d'AGV després de 24h. Durant la subseqüent digestió anaeròbia de fangs pre¬tractats (9-48 h), s'incremetà la producció de biogàs en un 30-40 %, treballant a 55 ºC i 10 dies de TRF. El rendiment de producció de biogàs fou un 30 % superior amb fangs pre-tractats (0.28-0.30 vs. 0.22 L·gVS¬1) i el contingut de metà al biogàs també fou superior (69 % vs. 64 %). La digestió anaeròbia termofílica de fangs pot donar lloc a una producció neta d'energia, durant estacions fredes i càlides, si s'utilitzen reactors amb aïllament tèrmic de les parets i amb recuperació energètica a partir del biogàs i dels fangs digerits. En aquest cas, l'eficiència energètica de reactors termofílics treballant a la meitat de TRF (10-15 dies) que reactors mesofílics (20-30 dies) seria similar, per la qual cosa el cabal diari podria ser doblat, o el volum del reactor reduït, amb el conseqüent estalvi en el cost de tractament dels fangs. A més, un sistema en dues etapes (70/55 ºC) produiria més energia neta que un sistema en una sola etapa (55 ºC) amb un TRF de 10 dies. De totes maneres, la quantitat d'energia neta generada augmenta amb el volum del digestor donat que, malgrat la disminució en la producció de metà a TRF creixents, la producció d'energia segueix essent superior al consum, i per tant com més quantitat de fangs hi hagi al digestor, més energia es produirà. / Energy consumption accounts for some 30 % of the total operating costs of intensive sewage treatment systems. In conventional wastewater treatment plants employing an activated sludge process, around 15-20 % of this energy is used in the sludge treatment line, including sludge pumping, thickening, stabilisation and dewatering. Therefore, optimisation of sludge management can substantially contribute in the reduction of wastewater treatment costs. Thermophilic anaerobic digestion is more efficient than mesophilic anaerobic digestion, in terms of biogas production, volatile solids (VS) removal and pathogens destruction. The process might be further accelerated by sludge pre-treatment, promoting sludge solubilization and hydrolysis. The aim of this PhD Thesis was to study the impact of process parameters on the thermophilic anaerobic digestion of sewage sludge, to evaluate the effect of implementing a low temperature pre¬treatment step, and to assess alternative processes from an energy perspective. The experimental results presented were obtained by operating two lab-scale reactors for almost two years. During this period, the effect of process temperature, sludge retention time (SRT), organic loading rate (OLR) and 70 ºC sludge pre-treatment on the anaerobic digestion of sewage sludge was studied. The process was evaluated in terms of energy production (i.e. biogas and methane production) and the quality of the effluent sludge (i.e. VS and volatile fatty acids (VFA) content, sludge dewaterability and hygienisation). Focus was put on the stability of the process at decreasing SRT and increasing OLR. Process efficiency during stable performance under each operating condition assayed was compared. Finally, the results were assessed from an energy perspective, by means of theoretical energy balances and ratios; and compared to the results obtained with experimental data from other studies. A first order kinetic model was also used. The conclusions drawn from the different issues dealt in this work are summarised as follows: During anaerobic sludge digestion, the transition from a mesophilic (43 ºC) to a thermophilic operation (50 ºC) may be carried out without disturbing the process, by operating the reactors at high SRT ( ≥ 30 days) and low OLR (≤ 0.5 kg VS m-3reactor d-1). Under such conditions, some VFA accumulation (0.5-2.5 g L-1) and enhanced pathogen destruction (residual E. coli ≤ 102 CFU mL-1) would be the main differences of thermophilic (50-55 ºC) compared to mesophilic (38-43 ºC) reactors. Thermophilic sludge digestion at 50 ºC and 55 ºC should be similar in terms of biogas production and effluent stabilisation, hygienisation and dewaterability; provided that other process parameters are the same. Methane production rate tends to increase proportionally to the OLR, thus to the SRT and VS concentration in the feed sludge. Similarly, the quality of the effluent sludge (VS content, VFA content and sludge dewaterability) is also affected by the OLR. According to the results obtained at 55 ºC, methane production rate increased by 2-3 times (from 0.2 to 0.4-0.6 m3CH4 m3reactor d-1) by decreasing the SRT from 30 to 15-10 days; increasing the OLR from 0.5 to 2.5-3.5 kg VS m3reactor d-1. However, process unbalance resulted from SRT reduction to 6 days, with OLR above 5 kg VS m3reactor d-1. The following concentrations might be useful to detect and prevent digester failure during thermophilic sludge digestion: total VFA (2.5 g L-1), acetate (0.5 g L-1), acetate/propionate ratio (0.5), intermediate alkalinity (1.8 g CaCO3 L-1), intermediate alkalinity/partial alkalinity ratio (0.9), intermediate alkalinity/total alkalinity ratio (0.5), methane content in biogas (55 %). The 70 ºC sludge pre-treatment may initially promote sludge solubilization, increasing the concentration of soluble to total organic matter from 5 to 50 % within 9-24 h; which is followed by a progressive VFA generation after 24 h. Subsequent anaerobic digestion of pre-treated sludge samples (9¬48 h) could increase biogas production by 30-40 % working at 55 ºC with a SRT of 10 days. Biogas yield is some 30 % higher with pre-treated sludge (0.28-0.30 vs. 0.22 L·gVSfed-1) and methane content in biogas is also higher with pre-treated sludge (69 vs. 64 %). Thermophilic anaerobic sludge digestion would result in net energy production, during cold and warm seasons, provided that digesters with wall insulation and with energy recovery from both the biogas produced and the effluent sludge are used. In this case, the energetic efficiency would be similar for thermophilic digesters working at half the SRT (10-15 days) of mesophilic digesters (20-30 days), meaning that the sludge daily flow rate could be doubled, or the reactor volume reduced, with subsequent savings in terms of sludge treatment costs. Furthermore, two-stage systems (70/55 ºC) may result in higher net energy production compared to single-stage systems (55 ºC) at 10 days SRT. However, the amount of surplus energy generated increases with digester volume. In spite of the decrease in methane production rate at increasing SRT, energy production is still higher than energy consumption, and therefore the bigger the amount of sludge in the digester, the higher the energy production.

Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographic references (p.91-111).

Includes bibliographical references (p. 62-73).

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 170-181). Also available in electronic version. Access restricted to campus users.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

No description available.