Improper waste handling of mixed municipal solid waste (MSW) without material and energy recovery leads to human health problems, environmental pollution, and loss of resources. In contrast, proper handling of these wastes can sustain a circular economy and support an effective and efficient waste management system that reduces the volume of wastes that go into the environment.
This thesis evaluated the decomposition and distribution of 2 key fractions of the waste stream, namely, organic wastes and plastics. The chemical properties of Municipal Solid Waste (MSW) composts made in Nigeria's wet and dry seasons were evaluated to determine their significant differences. These properties included pH, electrical conductivity (EC), organic matter (OM), carbon content, nitrogen content, C/N ratio, phosphorus, potassium, calcium, sodium, and magnesium contents. The heavy metals are chromium, copper, nickel, lead, zinc, and iron. The results revealed seasonal variations in the properties of compost made in Nigeria except for nitrogen content.
The results showed that pH, electrical conductivity (EC), organic matter (OM), carbon content and C/N ratio were significantly influenced by seasonality and higher in the wet season than in the dry season. Phosphorus, potassium, calcium, and heavy metals: chromium, copper, nickel, lead, zinc, and iron were significantly higher in the dry season than in the wet season, except for sodium and magnesium, which were slightly higher in the wet season than the dry season. Higher contents in the dry season were simply from dilution effects; they were leached out during the wet seasons. The EC of composts made in the wet and dry seasons were 4534.17 and 2631.58µScm-1, higher than the optimal values (750 to 2000 µScm-1). The reason for this is that the type of feedstock (food waste) used in composting was very high in water-soluble salts and will influence the activity of the microorganisms during composting.
The identification and distribution of plastic wastes were conducted in three dumpsites in Owerri, Imo State, in Nigeria. A total of 97, 117 and 129 unknown plastic wastes were collected from Irete, Orogwe and Nekede dumpsites. The unknown plastics were identified using Fourier transform infrared (FT-IR) spectroscopy, ascertaining if the weight of plastic materials was directly related to their mobility off-site (dumpsites). The result revealed that PP, PET and PE were the most abundant plastic polymer wastes (36, 27, and 25%) respectively in the three dumpsites, with the weight of the plastic wastes significantly influencing their movement away from the three dumpsites. The degradation of five plastics (Polyamide 6 (PA-6), Polyethylene terephthalate (PET), High-density polyethylene (HDPE), Low-density polyethylene (LDPE), and Polypropylene (PP)) was investigated in an open field in substrates; soil, compost, and leachate for 24 months in the UK and Nigeria and under laboratory conditions using directly three white-rot fungi (WRF), namely, Phanerochaete Chrysosporium, Ceriporiopsis Subvermispora and Trametes Versicolor, for 12 weeks. At different time intervals, these plastics were studied to track their degradation rate. The degradation study was monitored by visual observation, light microscopy, weight loss, FTIR, carbonyl index (CI), scanning electron microscopy (SEM), and tensile strength analysis.
Visual observation, light microscopy and SEM showed notable changes such as discolouration, roughness, grooves, and biofilm formation on the plastic surfaces, which altered the surface properties of plastics. Their weights fluctuated in the substrates, and with the WRF, HDPE
discs from Nigerian soil had the highest weight loss of 5 %, while PP had the most weight gain of 2.1 % from UK compost after 24 months. In the laboratory experiment with the WRF, the PA discs had the highest weight loss of 2% with T. Versicolor, while PP had the most weight gain of 1.3 % with T. Versicolor. The fluctuations were due to microbial activities or water absorbed from different environments. There were significant differences in weight loss and
reduction in the thickness of plastic discs over time in substrates used for
the study.
FTIR spectra and CI revealed reductions in the peak intensities, progressive shifts of peaks, disappearances, and formation of new peaks, which are attributed to oxidation, hydrolysis and depletion of the functional groups of the plastics. Lastly, the tensile strength of all plastics
decreased during the degradation study but at different rates. It was also significantly influenced over time in all the substrates used for the degradation study. PET had the highest loss in tensile strength, 22 %, in UK compost, while PP had the least loss in tensile strength, 0.1%, in UK soil after 24 months. These changes became more apparent at 18 and 24 months in substrates and 12 weeks with WRF, especially on the sides of the plastics affected by mechanical shearing.
This research provides underpinning evidence that the properties of MSW composts made in Nigeria were influenced by seasonality. Also, the degradation of synthetic plastics in substrates and white-rot fungi (WRF) was a slow process. It becomes necessary to consider follow-up research by introducing initiators that present new functional groups, thereby producing free radicals on the plastics that will modify and break up their long chains before biodegradation. Also, extending the plastic time in both substrates and WRF could be done to see if it will increase the degradability of plastics.