Physico-chemical and biological evolution of thermophilic compost as influenced by nitrogenous feedstock and duration
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Date
2024-10
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Kenyatta University
Abstract
Thermophilic composting is a source of agricultural enzymes, microbes, and nutrients from organic waste. Lantana camara, Tithonia diversifolia, and fresh grass (Pennisetum purpureum) clippings are readily available supplemental nitrogen sources in compost. However, their influence on microbes and physical-chemical state during the composting period has not been explored. This study sought to enumerate the influence of regimens of these materials and their duration on the evolution of the microbial communities and their physical-chemical and metabolic potential during composting using next-generation sequencing and gravimetric methods. Precisely, the objectives of this study were: (1). To evaluate the influence of composting materials and durations on compost physical-chemical quality; (2). To examine the impact of composting materials and duration on prokaryotic community structure; (3). To evaluate the influence of composting materials and duration on fungal and non-fungal eukaryotic community structure; (4). To enumerate the influence of composting materials and the composting duration on the metabolic potential of compost fauna. A completely randomized block design (CRBD) was adopted, involving the following compost treatments; (1). Cattle manure + Dry maize stalks + Lantana camara twigs (L), Cattle manure + Dry maize stalks + Tithonia diversifolia twigs (Tithonia), Cattle manure + Dry maize stalks + Grass clippings (G), and a mixture of the 3 treatments (LTG) composts. Sampling from triplicate compost heaps was mainly done at 21, 42, 63, and 84 days of composting as per standard procedures of each objective. Physical-chemical parameters such as temperature, nitrogen pH, and carbon were analyzed from triplicate heaps using standard gravimetric protocols. On the other hand, total community 16S rRNA, ITS, and 18S rRNA were also extracted using the ThermoFisher Scientific® microbiome kit before separate amplification and sequenced under the Illumina platform. Sequence bioinformatics was mainly done using Divisive Amplicon Denoising Algorithm v2 workflow. Total compost ribonucleic acid (RNA) was extracted using the trizol-based method, before shotgun sequencing under the Illumina miseq platform. This was followed by functional profiling based on the Metapro, and SAMSA2 bioinformatics workflows. Complementary functional profiling was also done based on 16S rRNA sequences using PICRUSt2 bioinformatics workflow. There were positive and negative correlations between various physical-chemical parameters, with temperature positively correlated with ammonia and carbon. Proteobacteria, Sordariomycetes, and Holozoa were the most dominant prokaryotic, fungal, and non-fungal eukaryotic classes respectively. The most significant prokaryotic and eukaryotic abundance, richness, and diversity were observed in Lantana-based compost which is attributable to its complexity compared to other materials. PcoA results showed distinct groupings as influenced by composting materials and duration with a total of 73%, 28%, and 66% variation of prokaryotes, fungi, and non-fungal eukaryotes respectively. Composting materials had no significant influence on most metabolic pathways. Composting days had a significant influence, with days 42 and 63 having the most sequences for carbon and nitrogen metabolism respectively. This study recommends that composting practices should focus on extending composting duration rather than varying feedstock types to improve compost quality and stability.
Description
A thesis submitted in fulfillment of the requirement for the award of the degree of doctor of philosophy (biotechnology) in the school of pure and applied sciences of Kenyatta University
October, 2024
Supervisors:
Prof. Steven runo
Prof. Maina mwangi
Dr. Anne kelly kambura