Browsing by Author "Mutegoa, Eric"

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Approaches to the mitigation of ammonia inhibition during anaerobic digestion – a review
(IWA Publishing, 2020-06-03) Mutegoa, Eric; Hilonga, Askwar; Njau, Karoli
The digestion process of organic waste rich in high ammonia content has always been a gridlock during methanogenesis process. The free ammonia may increase inhibition/toxicity, which in turn affects the microbial community in the digester and eventually leading to process failures. Substantial methods have been proposed and assessed for curtailing ammonia emissions in anaerobic digesters to attain a safe and steady process so that along with high methane production, high quality of effluents can also be recovered. There are several means for lowering the erratic ammonia in organic wastes which has been in use currently such as the decrease of pH, which favour the formation of ammonium over ammonia in the equilibrium. For example, the use of chemical additives that attach ammonium-N. Ammonia can also be removed from nitrogen-rich substrates during anaerobic digestion through other methods such as struvite precipitation, membrane distillation, air stripping, ion exchange, and adsorption. A thoroughly survey from different articles has shown that ion exchange, adsorption and changing of the C/N ratio through co-digestion technique, are the most commonly studied methods for mitigating ammonia inhibition in wastewater during anaerobic digestion. A detailed review of these methods in the context of nitrogen-rich substrates will be discussed in this paper.
Controlling ammonia and sulfide inhibition during anaerobic digestion of slaughterhouse waste
(NM-AIST, 2021) Mutegoa, Eric
The performance of experimental batch-reactor loaded with slaughterhouse waste at mesophilic temperature was investigated as well as the inhibition of both ammonia and sulfide in the aqueous phase during phase I of anaerobic digestion. The methylene blue method was used to quantify the amount of sulfide in the liquid phase whereby the amount of total ammonia nitrogen in the liquid phase was quantified by using Nessler method. The maximum CH 4 content of 69.6% was achieved at 0.37 VFA/Alkalinity ratio and pH of 7.51 during day 37 of anaerobic digestion. However, a sudden increase of ammonia nitrogen in the digester from day 44 to day 68 decreased the methane content by 62.15% from 65% to 24.6%. During phase II of anaerobic digestion, the efficacy of inorganic additives on the removal of total ammonia nitrogen and sulfide in the aqueous phase of slaughterhouse waste undergoing anaerobic digestion in the batch reactor was investigated for 65 days. A mixture of natural inorganic additives processed from the anthill and red rock soil samples collected from Arusha, Tanzania were used as adsorbents in different ratios. XRD analysis revealed that the anthill soil sample is endowed with quartz and hematite major mineral phases while red rock soil contains albite, pyroxene, and quartz as predominant phases. The anthill and red rock soil samples calcined at 900 ℃ displayed higher BET surface areas of 815. 35 and 852.35 m 2 /g, respectively. Among all the adsorbent ratios investigated at different calcination temperatures, the ratio of 1:1 and calcination temperature of 700℃ produced the highest adsorption capacities of both TAN and sulfide. Adsorption isotherm studies revealed that Jovanovich model fitted better to the experimental data than Langmuir and Freundlich models. The findings of this study have demonstrated that anthill and red rock soils can be exploited as affordable, ecofriendly and efficient adsorbents for mitigation of TAN and sulfide from the liquid phase and sustenance of methanogenesis.
Effect of mixing ratios of natural inorganic additives in removing ammonia and sulfide in the liquid phase during anaerobic digestion of slaughterhouse waste
(Elsevier, 2021-06-01) Mutegoa, Eric; Malima, N; Hilonga, Askwar; Njau, Karoli
In this study, the efficacy of inorganic additives in the removal of total ammonia nitrogen (TAN) and sulfide in the aqueous phase of slaughterhouse waste undergoing anaerobic digestion in the batch reactor was investigated. A mixture of natural inorganic additives processed from the anthill and red rock soil samples collected from Arusha, Tanzania were used as adsorbents in different ratios. These materials were chosen in regard to their abundance in the local environment, surface properties, and elemental composition. Before analysis, the materials were pulverized and calcined at 700 and 900 °C for 2 h in a furnace and then sieved to 250 μm fine particle size. XRD analysis revealed that the anthill soil sample is endowed with major mineral phases of quartz and hematite while red rock soil contains albite, pyroxene, and quartz as predominant phases. The anthill and red rock soil samples calcined at 900 °C displayed higher BET surface areas of 815.35 and 852.35 m2/g, respectively. The mixture of anthill soil and red rock soil in a ratio of 3:1 had a higher TAN removal efficiency of 92% at a contact time of 30 min compared to other ratios. On the other hand, a ratio of 1:2 showed a higher sulfide removal efficiency of 79% at a contact time of 60 min. Adsorption isotherm studies revealed that the Jovanovich model fitted better to the experimental data than the Langmuir and Freundlich models. The results demonstrated further that inorganic additives have a synergistic effect on stimulating methanogenesis as well as eliminating ammonia and sulfide during anaerobic digestion of slaughterhouse waste. Our findings demonstrate that anthill and red rock soils can be exploited as affordable, ecofriendly, and efficient adsorbents for mitigation of TAN and sulfide from the liquid phase and sustenance of methanogenesis.
Evaluating the level of ammonia and sulfide in the liquid phase during anaerobic digestion of slaughterhouse waste operating at mesophilic scale digester—the impact of inhibition and process performance
(AIMS Press, 2020-07-10) Mutegoa, Eric; Kandola, Isack; Hilonga, Askwar; Njau, Karoli
The performance of experimental batch-reactor loaded with slaughterhouse waste at mesophilic temperature was investigated as well as the inhibition of both ammonia and sulfide concentration in the aqueous phase. The digester was operated for 68 days by evaluating the process stability basing on controlling parameters such as pH, volatile fatty acids and alkalinity in relation to the methane produced. The maximum CH4 content of 69.6% was achieved at 0.37 VFA/Alkalinity ratio and pH of 7.51 during day 37 of anaerobic digestion. However, a sudden increase of ammonia nitrogen in the digester from day 44 to day 68 decreased the methane content about 62.15% from 65% to 24.6%. Similarly, as the amount of sulfide content decreased in the liquid phase, gaseous H2S was elevated up to 132 ppm in the 68th day. During this time, it was observed that the ratio of VFA/Alkalinity decreased to 0.16, with a very low concentration of VFA, which was 150.92 mg/L. This phenomenon indicated that all the acids produced were consumed by methanogens and ammonia inhibition was at the highest rate due to the increase of ammonia nitrogen concentration in the last days of digestion. Furthermore, among of peculiar characteristic shown by slaughterhouse waste is the ability to maintain the pH above 7 without the addition of any buffering agent throughout the AD process. Meanwhile, the evaluation of the level of both ammonia and sulfide in the aqueous phase revealed that the inhibitory effect of ammonia concentration was higher than sulfide concentration.
Preparation of activated carbon with disered properties through optimization of impregnating agent
(Rjeas, 2014) Mutegoa, Eric; Onoka, Isaac; Hilonga, Askwar
In this study, activated carbon with desired properties was prepared from peanut shell and sugarcane bagasse using chemical activation method in which potassium hydroxide (KOH) was used as a impregnating agent. The properties of the activated carbon were evaluated based on the activation temperature, yield percentage, ratio of KOH to Char impregnation, and iodine adsorption number. Based on the characterization methods employed, the desired properties for activated carbon from peanut shell were obtained at these optimum conditions: Activation temperature of 350 0 C, treatment time of 1hr, and impregnation ratio of 1:2. These conditions exhibited maximum iodine number of 355 mg/g. On the other hand, sugarcane bagasse produced the superior properties (iodine number of 914.71 mg/g) at an activation temperature of 700 0 C, treatment time of 1hr, and impregnation ratio of 1:1. The activated carbons with superior properties obtained in this study are suitable for the treatment of waste water associated with carboxylic acids. Our on- going project will test the performance of the final product for various innovative applications