Simon Mdondo Wandera - Academia.edu (original) (raw)

Papers by Simon Mdondo Wandera

Renewable Energy, Jul 1, 2022

Waste Management, May 1, 2022

Conventional mesophilic anaerobic digestion (AD) is widely used to treat animal manure, but patho... more Conventional mesophilic anaerobic digestion (AD) is widely used to treat animal manure, but pathogen inactivation remains a significant challenge. Thermophilic and hyperthermophilic hydrolysis pretreatment was thus introduced as a hygienization step in a two-stage anaerobic digestion process. Results from 100-day experiments showed culturable Escherichia coli (E. coli) reduction was up to 6.9 log10 through a hygienization step, but RT-qPCR tests showed much less reduction in viable E. coli. The difference between viable and culturable cells revealed the complexity in pathogen inactivation. High-throughput sequencing indicated that the second stage in the two-stage AD further reduced the relative abundance of pathogens, including Enterococcus, Streptococcus, and Acinetobacter, while Clostridium_sensu_stricto still exhibited high relative abundance. Thermophilic hygienization induced a 6.7% increment in methane production, while hyperthermophilic pretreatment showed minimal effect on methane production. Focusing on the energy recovery and environmental safety point of view, the introduction of an integrated system incorporating the thermophilic and two-stage anaerobic process is recommended.

Bioresource Technology, Dec 1, 2021

The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining proc... more The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining process stability. A hybrid submerged anaerobic membrane bioreactor (AnMBR), integrating 27%(v/v) polyurethane sponge as fixed carriers were therefore investigated at (50 ± 2) °C. The organics removal efficiencies, COD mass balance, and membrane filtration performance were investigated in a 75-days continuously operated experiment. The results showed that methane production reached 0.31 L/(kg·COD) under an organic loading rate of 7.3 kg·COD/(m3·d). The low concentration of total volatile fatty acids of 247 ~ 274 mg/L and a high proportion of Methanosarcina (>97%) represented the high stability of the thermophilic process. Approximately 21% of biomass grew on the carriers in the hybrid AnMBR and induced a much lower suspended solids concentration and viscosity of bulk sludge. Noticeable lower trans-membrane pressure was consequently observed. The affecting factors identified by PCA analysis proved the advantages of the hybrid AnMBR for alleviating membrane fouling formation.

Bioresource Technology, 2018

Energy Conversion and Management, Sep 1, 2019

Bioresource Technology, Sep 1, 2018

Sustainability

Slow hydrolysis persistently affects the anaerobic digestion of animal manure. Thermophilic and h... more Slow hydrolysis persistently affects the anaerobic digestion of animal manure. Thermophilic and hyper-thermophilic treatments introduced into a two-stage anaerobic process treating pig manure were investigated, with a single-stage mesophilic process as a control. The results from the 100-day experiment showed the thermophilic-mesophilic system had the highest removal efficiency of volatile solids at 60.8%, 18% higher than the single-stage process. The thermophilic and hyper-thermophilic hydrolysis reactors contributed 23.5% and 21.7% solubilization of chemical oxygen demand (COD), respectively. The hydrolysis efficiency achieved in the single process was 49.7%, which was lower than the hydrolysis in the two-stage processes. Approximately 60% of COD was distributed in the solid fraction in the first stage, and more than half of the particle COD continued to hydrolyze in the subsequent second stage. The mass balance of COD and volatile solids removal performance illustrated the advant...

Bioengineered, 2022

ABSTRACT Animal manure is the main source of bioenergy production by anaerobic digestion (AD). Ho... more ABSTRACT Animal manure is the main source of bioenergy production by anaerobic digestion (AD). However, the pathogenic bacteria in manure may pose a high risk to human health by contaminating the environment if not effectively inactivated during AD. Worldwide, more than 20,000 biogas plants are running for the treatment of animal manure. AD has been playing the important role in establishing a circular economy in the agricultural sector and may contribute to the United Nations sustainable development goal (UN SDG). Nevertheless, whether AD is a reliable approach for pathogens inactivation has been challenged. A comprehensive understanding of the coping mechanisms of pathogens with adverse conditions and the challenges of establishing the AD process to inactivate effectively pathogens are yet to be analyzed. In this review, the diversity and resistance of pathogens in animal manure are summarized. The efficiencies and the difficulties of their inactivations in AD are also analyzed. In particular, three forms of pathogens i.e. sporing-forming pathogens, viable but non-culturable (VBNC) pathogens, and persistent pathogens are discussed. The factors influencing the pathogens’ inactivation and AD efficiencies are analyzed. The trade-off between energy production and pathogens inactivation in an AD system was consequently pointed out. This review concluded that the development of anaerobic processes should meet the goals of high efficient bioenergy production and deep hygienization.

$Research paper thumbnail of The materials flow and membrane filtration performance in treating the organic fraction of municipal solid waste leachate by a high solid type of submerged anaerobic membrane bioreactor$

Bioresource Technology, 2021

The anaerobic digestion of leachate from organic fraction of municipal solid waste (OFMSW) is a l... more The anaerobic digestion of leachate from organic fraction of municipal solid waste (OFMSW) is a long-standing challenge. A submerged anaerobic membrane bioreactor (AnMBR) embedding three flat sheet membrane was therefore continuously operated for 63 days to investigate the materials flow and membrane performance. The results obtained show that approximately 90% COD was removed and 86% was converted into methane under an OLR of 5.6 kgCOD/m3·d corresponding to a HRT of 10 days. Under the high solid condition (34.5-61.1 g/L total solids in AnMBR) and flux of 5 and 6 LMH, the membranes was operated practically at constant trans-membrane pressure (TMP). When the membrane was operated at a high flux of 7 LMH the TMP rapid increase occurred in 22 h resulting in a non-recoverable permeability. A sustainable flux was thus identified. This study demonstrated the feasibility of AnMBR treating OFMSW leachate under high solid condition with high flux.

Water Science and Technology, 2019

Trace elements play a critical role for microbial activity in anaerobic digestion (AD) but their ... more Trace elements play a critical role for microbial activity in anaerobic digestion (AD) but their effects were probably overestimated in batch tests and should be comparably evaluated in continuous systems. In this study, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ were added in different concentrations to manure wastewater, and the effects were compared in both batch and continuous systems. The results were used to demonstrate suitable trace element compositions for AD of dairy and swine wastewater, and to compare the outcomes from batch and continuous systems. Fe2+ and Zn2+ were identified as being the most efficient stimulant of dairy and swine wastewater respectively. The addition of 5 mg/L Fe2+ and 0.4 mg/L Zn2+ increased the batch specific methane yield by 62% and 126% for dairy and swine wastewater, respectively. Nevertheless, a lower increment of 2% and 21%, for dairy and swine wastewater was obtained in the 120-day continuously-fed experiments. The 16S rRNA gene sequencing results indic...

Science of The Total Environment, 2019

Energy Conversion and Management, 2019

Bioresource Technology, 2019

International Biodeterioration & Biodegradation, 2019

Renewable Energy, 2018

Biogas plants have been widely used to both reclaim bio-energy from agricultural waste and to tre... more Biogas plants have been widely used to both reclaim bio-energy from agricultural waste and to treat waste; however, the efficiency of these biogas plants has yet to be determined. In this study, the performance of five full scale biogas plants treating chicken manure (CM), pig manure (PM), a mixture of chicken and pig manure (MM), dairy manure (DM), and maize straw (MS) were investigated. The results showed that CM had the highest total energy (16.4 KJ/g-TS) and the MM had the highest bio-available energy (10.2 g-COD/g-TS). The CM plant adopted a suitable hydraulic retention time (HRT) but the other plants used a much longer HRT than necessary. The methane production from CM, PM, MM, and DM was improved by 12%, 22%, 32% and 25% with the addition of trace metals, and this also resulted in an increment in the methanogenic activity for CM, PG, MM and MS. The pH stability of all the biogas plants was maintained at an acceptable level; nevertheless, the high pH and ammonium in the CM digester negatively affected the methanogenic activity. The results, therefore, conclusively indicated that the operation of the biogas plants could be more effective.

Bioresource technology, 2018

The impact of temperature on the anaerobic digestion of chicken manure was investigated by studyi... more The impact of temperature on the anaerobic digestion of chicken manure was investigated by studying the process performance and pathway for continuously-fed digesters under mesophilic and thermophilic conditions. The mesophilic digester obtained a 15% higher methane yield compared with the thermophilic digester. Mesophilic and thermophilic digester had free ammonia of 31 and 145 mg/L, respectively. The stable carbon isotope analysis indicated that 41% and 50% of acetate was converted to methane through the syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway under mesophilic and thermophilic conditions, respectively. The genus Pseudomonas represented 10% and 16% under mesophilic and thermophilic conditions, respectively. A high abundance of the methanogens genus Methanoculleus (94% of total methanogens) in mesophilic and the genus Methanothermobacter (96%) in thermophilic digesters indicated they were the main hydrogenotrophic partners in SAO. The presen...

Bioresource technology, Jan 18, 2017

Anaerobic digestion (AD) of FW shows instability due to both the presence of high lipids and accu... more Anaerobic digestion (AD) of FW shows instability due to both the presence of high lipids and accumulation of volatile fatty acids. In this study, AD of food waste (FW) was optimized by removing lipids (LRFW) and by co-digestion with sewage sludge (1:1w/w on dry matter). The results obtained showed that lipids extraction increased FW methane yield from 400 to 418mL-gVSadded(-1) under mesophilic conditions (35°C) and from 426 to 531mL-gVSadded(-1) in thermophilic conditions (55°C). Two degradation phases (k1 and k2) described FW and LRFW degradation. In the thermophilic, LRFW-k1 (0.1591d(-1)) was slightly higher than that of FW (k1 of 0.1543d(-1)) and in the second stage FW-k2 of 0.0552d(-1) was higher than that of LRFW (k2 of 0.0117d(-1)). The majority of LRFW was degraded in the first stage. FW and sewage sludge co-digestion reduced VFA accumulation, preventing media acidification and improving process stability.

Bioresource Technology, 2016

Science of The Total Environment, 2016