Country-level assessment of agrifood waste and enabling environment for sustainable utilisation for bioenergy in Nigeria.

It is essential to plug inefficiencies due to agrifood losses and wastes, which pose a significant threat to the sustainable supply of nutritional agrifood commodities/products. Country-specific evaluations of the extent of agrifood losses/wastes, including the pathways and impacts on net agrifood production, are crucial to inform interventions, research, policies and investments. This kind of knowledge is scarce in sub-Saharan Africa (SSA) countries, many of which are food insecure. This paper presents an estimation of and the bioenergy potential for agrifood loss and waste (AFW) - the edible and inedible residual biogenic fractions of crops and animal commodities/products - in Nigeria. Our findings reveal that Nigeria generates 183.3 ± 8.9MT of AFW per annum. About 27% of the average annual total domestic supply of edible agrifood commodities/products is lost before reaching markets/consumers. The intrinsic bioenergy potential of the inedible AFW fraction generated annually in Nigeria is estimated to be 1,816.8 ± 117.3PJ; this is sufficient to meet 2030's bioenergy targets and replace a third of its total (grid, off-grid and self-generation) supply targets. However, Nigeria lacks regulatory, policy and institutional frameworks specific to AFW management. This study recommends a sustainable approach to managing AFW, addressing the interlinked challenges of bioenergy production, public health and environmental sustainability. Besides addressing knowledge gaps in the Nigerian agrifood sector, the information generated in this study is well-timed to inform decision-making and policy formulation on decentralised AFW-based bioenergy interventions to achieve energy supply targets in the country by 2030 and beyond. This study is also strategic to guide future research/interventions that align with AFW utilisation/clean energy generation in SSA.

Stabilization/solidification of acid tars.

This work involve a systematic treatability study of the treatment of acid tars (AT), a waste generated during the processing of petroleum and petrochemical, by stabilization/solidification with Portland cement (CEM I), with the addition of high carbon fly ash (HCFA), an industrial by-product, as a novel sorbent for organic contaminants. A factorial design experiment was adopted to investigate the effects of organic content, HCFA:AT ratio, percentage CEM I addition, and curing time on response variables including unconfined compressive strength (UCS), hydraulic conductivity, porosity, and leachability-related properties of the stabilized/solidified (s/s) products, and to assess management options for the s/s products based on performance criteria adapted from regulatory and other guidance. Results show that all studied factors had significant effects on the tested properties of the s/s products. Acid tar reduced UCS, but strength increase was observed with increased curing time. Increased HCFA addition led to an improvement in hydraulic conductivity. Assessment of management options indicates that the treated acid tars could find application as controlled low-strength materials, landfill liner, and landfill daily cover. The work demonstrates how a systematic treatability study can be used to develop a S/S operating window for management of a particular waste type.

Stabilization/solidification of petroleum drill cuttings.

A systematic treatability study was conducted for the treatment of drill cuttings, a waste generated during petroleum exploration and production, by stabilization/solidification with Portland cement (CEM I), with the addition of high carbon power plant fly ash (HCFA), an industrial by-product, as a novel sorbent for organic contaminants. A factorial design experiment was adopted to investigate the effects of waste-to-binder ratio, binder formulation, and curing time on response variables including unconfined compressive strength (UCS), hydraulic conductivity, porosity, leachate pH, and acid neutralization capacity (ANC) of the s/s products. Results show that all factors had significant effects on the properties of the s/s products. Drill cuttings and HCFA addition both reduced UCS, but HCFA improved hydraulic conductivity, relative to CEM I only s/s products. Drill cuttings addition had little effect on the ANC of products prepared with CEM I only, and improved that of products containing HCFA. Management options assessment based on performance criteria adapted from regulatory and other guidance suggests that the s/s products could find application as controlled low-strength materials, landfill liner, and landfill daily cover. This work demonstrates how a systematic treatability study can be used to develop a s/s operating window for the management of a particular waste type.

Stabilization/solidification of petroleum drill cuttings: leaching studies.

This work explores the effectiveness of Portland cement (CEM I), with the addition of high carbon fly ash (HCFA), as a novel binder, for the improvement of leachability-related properties of stabilized/solidified (s/s) petroleum drill cuttings. A factorial design experiment was adopted to investigate the effects of waste-to-binder ratio, HCFA addition, and curing time on leachate pH, acid neutralization capacity (ANC), and metal, chloride and hydrocarbon leaching. The leachate pH and ANC of all products suggested successful formation of a calcium-silicate-hydrate-based matrix with good resistance to acid attack, and little detrimental effect from drill cuttings addition. Leaching of amphoteric metals was significantly affected by pH, which was a function of other studied factors. All studied factors also affected leaching of chloride and hydrocarbons. CEM I, without HCFA addition, was more effective in immobilizing chlorides, but the overall chloride immobilization was poor in all runs. HCFA addition significantly reduced the leaching of hydrocarbons. Comparison of milligram of contaminant leached per kilogram of drill cuttings from the s/s products and untreated drill cuttings provided clear evidence of hydrocarbon and chloride immobilization. This work shows that HCFA improved the immobilization of organic contaminants and may represent an inexpensive binder for stabilization/solidification of organic wastes.

Characterization of acid tars.

Acid tars from the processing of petroleum and petrochemicals using sulfuric acid were characterized by gas chromatography/mass spectrometry (GC/MS), inductively coupled plasma/optical emission spectrometry (ICP/OES), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrometry, and scanning electron microscopy/energy dispersive X-ray (SEM/EDX) micro-analysis. Leaching of contaminants from the acid tars in 48 h batch tests with distilled water at a liquid-to-solid ratio 10:1 was also studied. GC/MS results show that the samples contained aliphatic hydrocarbons, cyclic hydrocarbons, up to 12 of the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs), and numerous other organic groups, including organic acids (sulfonic acids, carboxylic acids and aromatic acids), phenyl, nitrile, amide, furans, thiophenes, pyrroles, and phthalates, many of which are toxic. Metals analysis shows that Pb was present in significant concentration. DSC results show different transition peaks in the studied samples, demonstrating their complexity and variability. FTIR analysis further confirmed the presence of the organic groups detected by GC/MS. The SEM/EDX micro-analysis results provided insight on the surface characteristics of the samples and show that contaminants distribution was heterogeneous. The results provide useful data on the composition, complexity, and variability of acid tars; information which hitherto have been scarce in public domain.