Energy shortfall and air pollution are some of the challenges the human kind is facing today. Fossil fuel is still the most widely used fuel, which is a non-renewable resource, increasing excess carbon dioxide into the air. To overcome these issues, and reduce the carbon footprint, a greater development of renewable energy from green and natural resources is required. Compared to fossil energy, renewable energy has the benefit to reduce greenhouse gas emissions. There are different solutions available for green and renewable energy. Biomass is all biologically produced matter. Through the biological breakdown of biomass, biogas can be produced through the process called anaerobic digestion. This work was focused on the production of biogas, using algal biomass, sewage sludge and coffee grounds in an anaerobic co-digestion system. The main goal of this study was to investigate the feasibility of combining these three substrates. Two different types of algae were employed; Chlorella vulgaris and Scenedesmus sp. and the investigations included even the cultivation and harvesting of algal biomass. The production of biogas was examined under anaerobic conditions using 5 batch reactors in duplicate under constant temperature of 37 °C in 30 days. The result showed that co-digestion of algal biomass with sewage sludge led to an enhanced biogas production by 75 % compared to that of just sewage sludge. This indicates the synergistic effects of co-digestion. However, the addition of coffee ground to the mixture lowered the biogas production. All mixtures except the two with coffee grounds were in neutral pH. Methanogens, involved in the last step in biogas production are very sensitive to pH, and pH around 7 is the optimal for their activity. Furthermore, the presence of caffeine in the coffee ground could also inhibit the biogas production.

The main focus of this diploma thesis is the utilization of spent coffee ground (SCG) and its biorefinery products in agriculture primarly as a prospective organic fertilizer. The study verifies an influence of the addition of native SCG as well as its acid hydrolysed, defatted and oxidized forms to experimental clay soil on chemical and physical properties (ph, conductivity and mineral content). Growing experiments were realized by using Lactuca sativa to detect positive or negative effects on growth. Samples of basic soil and soil with the addition of commercial NPK fertilizer served as a reference to measuring data. Measurements showed that addition of SCG and products of its biorefinery to the soil caused a decrease of pH and an increase of conductivity of soil samples. Significant increase of extractable calcium, magnesium, manganese and moderate increase of potassium content was detected. 2 % addition of SCG to soil had no impact on plants growth. The number and visual appearance of lettuces were comparable with plants in basic soil. No seed on acid hydrolysed samples germinated, which was caused by an increase of conductivity and sulphate content in these samples. In defatted and oxidized samples the early germination and the highest number of lettuces was observed. The low content of phosphorus in all soil samples had a great impact on growth rate and visual appearance of cultivated lettuces. In comparison with soil with NPK addition, lettuces in samples with SCG and its form had a pink-grey colour and lower growth.

Coffee grounds are one of the very valuable lignocellulosic wastes that have been able to be processed and used for isolated phenolic substances. Many phenolic substances isolated from lignocellulosic wastes have antimicrobial properties. Aim of this thesis is isolation phenolic substances from spent coffee grounds extract and their available antimicrobial properties. Two isolation ways were applied to receive phenolic substances from spent coffee grounds: 1) solvent extraction (hexane, 75% ethanol, 70% acetone, diethyl ether, and ethyl acetate) and 2) release of active substances by alcoholic fermentation. All isolated materials were characterized by the viewpoint of concentration of reducing sugars, polyphenols and flavonoids. Subsequently, their antimicrobial activity was determined by using agar diffusion and broth dilution methods. Two gram-positive bacteria (Bacillus subtilis and Micrococcus luteus), one gram-negative bacteria (Serratia marcescens) and two yeasts (Candida glabrata and Saccharomyces cerevisiae) were used for antimicrobial testing. High-performance liquid chromatography (HPLC) was used to identify phenolic substances in the extracts. First, the results showed that the isolated sample with the highest antimicrobial activity was 70% acetone extract. This extract contained chlorogenic acid, gallic acid, caffeic acid and coumaric acid according to HPLC. The ethyl acetate extract showed the lowest antimicrobial activity. Second, after lyophilization, the isolated materials also revealed high antimicrobial activity. The highest antimicrobial activity displayed the materials obtained by the extraction with 70% ethanol. This sample contained chlorogenic acid, gallic acid and caffeic acids. Next, samples with phenolic compounds were obtained by the alcoholic fermentation of spent coffee grounds. These samples showed similarly to the previous solution extracts significant antimicrobial activity. Interestingly, the unfiltered samples received directly after alcoholic fermentation also showed antifungal properties. The characterization of phenolic compounds by HPLC showed similarly as in previous examples that chlorogenic, caffeic and gallic acids were present in these samples.

Recently, Sustainable engineering has become a necessity due to the limited availability of virgin materials, environmental concerns, and the lack of economic resources. According to the United Nations, "Sustainable engineering is the process of using resources in a way that does not compromise the environment or deplete the materials for future generations." However, developing cost-efficient and long-term road infrastructure has always been a challenge. Therefore, novel solutions are required to extend the pavement life cycle and minimize raw materials utilization to overcome this challenge. This research focuses on integrating the waste material to produce rheological engineered asphalt mixtures as pavement material. This study utilized three wastes, which are Off-spec fly ash (OFA), Reclaimed Asphalt Pavement (RAP), and finally, a bio-oil extracted from Spent Coffee Ground (SCG). OFA is a viable source for recycling due to the quantities produced yearly and deposited in landfills. For many years fly ash has been effectively used as a partial replacement for Portland cement in producing different types of concrete, embankments, and soil stabilization. Most of the underutilized fly ash is Off-Spec. That was the motive behind adopting the OFA in this study. This study aims to investigate the fly ash's interaction with the asphalt binder as an additive rather than a filler. Few studies evaluated this hypothesis regarding fly ash as an additive. Moreover, this research's novelty comes as there is a lack of research evaluating the fly ash-asphalt physio-chemical interaction. RAP utilization in roads infrastructure became a current state of practice. Most state Departments of Transportation (DOTs) have been using RAP at a composition average of about 20% of the mix by mass. This study focuses on maximizing the utilization of the RAP content through using a bio-oil extracted from the SCG as a new promising rejuvenator. Spent coffee ground is not well recycled, and almost six million tons are sent to landfills every year. This waste was found to release methane into the atmosphere; methane is the second-most abundant greenhouse gas and has a global warming potential up to 86 times greater than CO2, which is highly harmful to the environment. In this study, the overreaching goal is to develop a green, innovative, and sustainable approach by recycling three different types of wastes (OFA, RAP, and SCGO) to achieve high-performance asphalt pavements. In addition, this study documents the science-based approach to successfully integrating these wastes as substitutes to the asphalt binder. Results show that some OFAs are associated with improved rheological performance, damage healing, and cracking resistance as an asphalt binder additive. The improvement is attributed to the level of interaction between the binder and the physical and chemical characteristics of the OFA. The use of rejuvenators further improved the aging resistance of the ash blends, suggesting high potential synergy, especially the proposed SCGO rejuvenator, which promotes utilizing it as a promising eco-friendly rejuvenator in the asphalt pavement industry. After engineering a product built by OFA and rejuvenators, these results have been validated by mixtures’ scale testing. 62% optimum RAP content is suggested to be utilized with an 11% dosage of the proposed SCGO rejuvenator as binder replacement. For the new engineered OFA/rejuvenators products, a 30% optimum RAP content is suggested to be used. Finally, Life Cycle Assessment (LCA) is conducted to evaluate the environmental potential of utilizing multi recycled materials in the Hot Mix Asphalt (HMA) industry. The results show a reduction in environmental impacts with RAP utilization and the new eco-friendly products (OFA and SCGO rejuvenator). Shifting HMA plant fuel to natural gas instead of Heavy Fuel Oil (HFO) offers considerable potential environmental benefits. Adopting the Ultrasonic Assisted-oil Extraction (UAE) as SCGO rejuvenator extraction method showed less energy and solvent consumption than the Soxhlet extraction, resulting in less environmental impacts. / Civil Engineering

Thesis (M.Sc. Agriculture. (Soil Science)) -- University of Limpopo, 2022 / The constant growth experienced by the coffee industry has led to the high-volume production of coffee waste worldwide. One of the main coffee wastes is spent coffee ground (SCG), a residue obtained after the ground coffee beans are treated under pressure. The present study was aimed to investigate the utilization of SCG to amend soil physicochemical properties. This study was conducted at Greenhouse Biotechnologies Research Centre of Excellence, University of Limpopo, South Africa, where the effect of various rates of SCG concentration in volume percentage (vol%) was tested for a period of nine months. The spent coffee ground residue was collected from four restaurants at Haenertsburg, and the application rates were 0, 5, 10, 20, 30, 50 vol%. To evaluate the change in soil physicochemical properties overtime, the incubation period was divided into four test periods namely T1 was after a month, T3 after 3 months, T6 after 6 months, and T9 after 9 months. Physicochemical properties including nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), total organic carbon (TOC), cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn), and lead (Pb), pH, electrical conductivity (EC), C:N ratio, large macroaggregates (LM), small macroaggregates (sM), microaggregates (m), unaggregated silt and clay (s+c), mean weight diameter (MWD) and soil moisture content (SMC) were quantified at the end of each test period. Results revealed that the interaction between incubation periods and various SCG application rates significantly (p<0.05) increased pHw, EC, MWD, LM, base cations and significantly decreased TOC, heavy metals, SMC, m, and sM. Spent coffee ground increased pHw and EC of the soil at all application rates and reached a maximum of 7.8 units at T6 in treatment SCG-5 and 202.30 S/cm at T9 in treatment SCG-50 above the control respectively. Total organic carbon increased by 548% above control in the highest treatment (SCG-50) at T1, but, however, started declining from T3 in all treatments across the incubation period. SCG’s highest application rates (SCG-20 to SCG-50) reduced the soil Cd toxicity (threshold of >2 mg/kg), but however, also reduced the availability of micronutrients (Cu and Zn) during the incubation period. At T9, Mg, Ca, K, and P increased from mean values of 55.9 to 77.9, 40.9 to 62.2, 77.4 to 112, and 22.0 to 30.0 mg/Kg above control in treatments with high application rates. LM increased whilst sM, and m decreased across the incubation period in all treatments. MWD increased by 46% at T1 and reached its maximum of 56% at T6 in treatment SCG-50 above control. Additionally, there was a positive relationship between LM and MWD. Soil moisture content however increased to 60.26% at T1 in treatment SCG-50 and decreased from T3 across the incubation period. Spent coffee ground has the potential to be used as a liming material, a chelating agent, and for water management in semi-arid areas. It retains and cycles nutrients and improves soil structure through aggregation. However, research should be done in field conditions to access the effectiveness of this residue. / NRF