Mesophilic anaerobic co-digestion of poultry dropping and Carica papaya peels: Modelling and process parameter optimization study

Biogas from lignocellulosic feedstock: current status and challenges

The organic wastes and residues generated from agricultural, industrial, and domestic activities have the potential to be converted to bioenergy. One such energy is biogas, which has already been included in rural areas as an alternative cooking energy source and agricultural activities. It is produced via anaerobic digestion of a wide range of organic nutrient sources and is an essential renewable energy source. The factors influencing biogas yield, i.e., the various substrate, their characteristics, pretreatment methods involved, different microbial types, sources, and inoculum properties, are analyzed. Furthermore, the optimization of these parameters, along with fermentation media optimization, such as optimum pH, temperature, and anaerobic digestion strategies, is discussed. Novel approaches of bioaugmentation, co-digestion, phase separation, co-supplementation, nanotechnology, and biorefinery approach have also been explored for biogas production. Finally, the current challenges and prospects of the process are discussed in the review.

Applications of artificial intelligence in anaerobic co-digestion: Recent advances and prospects

Anaerobic co-digestion (AcoD) offers several merits such as better digestibility and process stability while enhancing methane yield due to synergistic effects. Operation of an efficient AcoD system, however, requires full comprehension of important operational parameters, such as co-substrates ratio, their composition, volatile fatty acids/alkalinity ratio, organic loading rate, and solids/hydraulic retention time. AcoD process optimization, prediction and control, and early detection of system instability are often difficult to achieve through tedious manual monitoring processes. Recently, artificial intelligence (AI) has emerged as an innovative approach to computational modeling and optimization of the AcoD process. This review discusses AI applications in AcoD process optimization, control, prediction of unknown input/output parameters, and real-time monitoring. Furthermore, the review also compares standalone and hybrid AI algorithms as applied to AcoD. The review highlights future research directions for data preprocessing, model interpretation and validation, and grey-box modeling in AcoD process.

A review on anaerobic digestion with focus on the role of biomass co-digestion, modelling and optimisation on biogas production and enhancement

The status, recent trends and future perspectives in modelling and optimisation of anaerobic co-digestion is investigated. Areas that can be focused on and those which need further research towards enhancing biogas production are pointed out. Co-digestion, modelling and optimisation of anaerobic digestion as well as techno-economic aspects are reviewed in this paper. It was noted that co-digestion requires more research into a variety of bio-resources and their specific blend proportions. Modelling and optimisation of co-digestion with substrate seasonal fluctuations has not been addressed in previous studies. Controlling key process factors including temperature, pH, and carbon to nitrogen ratio is critical in improving biogas yield. Biogas hybridisation is yet to be explored in depth. The majority of researches are focused on mono-digestion, feedstock co-digestion, modelling, and optimisation of anaerobic digestion needs significant further investigations. A multi-objective approach taking all technical and economic parameters in the modelling and optimization is essential.

Optimization of biogas yield from anaerobic co-digestion of corn-chaff and cow dung digestate: RSM and python approach

The utilization of various feedstocks of unique characteristics in producing biogas could potentially enhance the application of clean fuel from biomass wastes. Two modelling tools were used to explore biogas production from plant and animal wastes. In this study, corn chaff was inoculated with cow dung digestate using different mixing ratios of substrate/inoculum (S/I) of 1:1, 1:1.55, and 1:3.5 for hydraulic retention time (HRT) of 25, 31, and 37 days as modelled using Central Composite Design (Face Centered Design) to optimize the process and predict the optimal response. The result shows that the mixture ratio of 1:1.55 for 37 days gave a cumulative highest biogas yield of 6.19 L under mesophilic conditions. The model p-value is <0.0001, an indication that the model term is significant. The python coding of the input factors gave the optimal value of 4.71 L, which is similar to the result obtained via CCD. Thus, both CCD (Face Centered Design) and python coding are reliable in the optimization of biogas production as they both predicted the same optimal values and approximately the same highest cumulative biogas yield. The GC-MS characterization of produced biogas revealed that it contains 68% methane and 22.76% CO₂. Other constituents present are confirmed by FTIR analysis results. The methane in produced biogas has a flashpoint of -182 °C, which is extremely flammable. This data shows that both CCD and python coding can model biogas production with high accuracy and biogas produced can be used for heating purposes.

Synergistic ammonia and fatty acids inhibition of microbial communities during slaughterhouse waste digestion for biogas production

The slaughterhouse waste (SHW) contains high organics which makes SHW a feasible feedstock for anaerobic digestion (AD). The present study systematically assessed the microbiome response and biomethanation along with the production of volatile fatty acids (VFAs) and ammonia under 2%, 4%, 6%, and 8% (w v^-1) loadings of SHW in AD. The optimum loading was 2% SHW which resulted in maximum biomethane production and VFAs consumption. A higher SHW concentration (4% and 6%) resulted in a prolonged lag-phase and decreased biomethane production. High VFAs (28.88 g L^-1) and ammonia nitrogen (>4 g L^-1) accumulation were observed at 8% SHW leading to permanent inhibition of biomethane and methanogenic archaea. An increase in ammonia and VFAs concentration, at 4% and 6% SHW loadings, shifted the methanogenic pathway from acetoclastic to hydrogenotrophic lead by Methanoculleus. Acetoclastic Methanosaeta (77.15%) dominated the reactors loaded with 2% SHW resulting in the highest biomethane production.

Biogas production from anaerobic co-digestion using kitchen waste and poultry manure as substrate-part 1: substrate ratio and effect of temperature

The rapidly declining fossil fuels are no longer able to meet the ever-increasing energy demand. Moreover, they are considered responsible for greenhouse gas (GHG) emission, contributing to the global warming. On the other hand, organic wastes, such as kitchen waste (KW) and poultry manure (PM), represent considerable pollution threat to the environment, if not properly managed. Therefore, anaerobic co-digestion of KW and PM could be a sustainable way of producing clean and renewable energy in the form of biogas while minimizing environmental impact. In this study, the anaerobic co-digestion of KW with PM was studied to assess the rate of cumulative biogas (CBG) production and methane percentage in four digester setups (D1, D2, D3, and D4) operated in batch mode. Each digester setup consisted of five parallelly connected laboratory-scale digesters having a capacity of 1 L each. The digester setups were fed with KW and PM at ratios of 1:0 (D1), 1:1 (D2), 2:1 (D3), and 3:1 (D4) at a constant loading rate of 300 mg/L with 50 gm cow manure (CM) as inoculum and were studied at both room temperature (28 °C) and mesophilic temperature (37 °C) over 24 days. The co-digestion of KW with PM demonstrated a synergistic effect which was evidenced by a 16% and 74% increase in CBG production and methane content, respectively, in D2 over D1. The D3 with 66.7% KW and 33.3% PM produced the highest CBG and methane percentage (396 ± 8 mL and 36%) at room temperature. At mesophilic condition, all the digesters showed better performance, and the highest CBG (920 ± 11 mL) and methane content (48%) were observed in D3. The study suggests that co-digestion of KW and PM at mesophilic condition might be a promising way to increase the production of biogas with better methane composition by ensuring nutrient balance, buffering capacity, and stability of the digester.

Crop performance and soil fertility improvement using organic fertilizer produced from valorization of Carica papaya fruit peel

In recent times, research attention is focusing on harnessing agricultural wastes for the production of value-added products. In this study, the valorization of Carica papaya (Pawpaw) fruit peels was evaluated for the production of quality organic fertilizer via anaerobic digestion (AD) while the effects of the fertilizer on maize crop were also assessed. Pawpaw peel was first pretreated by thermo-alkaline methods before AD and analyses were carried out using standard methods. The resulting digestate was rich in nutrients and was dewatered to form solid organic fertilizer rich in microbes and soil nutrients. When applied to maize plants, organic fertilizer showed a better effect on plant traits than NPK 15–15–15 fertilizer and without fertilizer application. These were more pronounced at mid to high organic fertilizer applications (30-to-60-kg nitrogen/hectare (kg N/ha)) rate. Comparison between the values obtained from the field experiments reveals that the organic fertilizer showed better performance in all parameters such as the number of leaves, leaf area, plant height, stem girth, total shoot, and root biomass, and length of the root. However, the chemical fertilizer outperformed all the organic fertilizer applied rates in the average highest size of the corn ear by 1.4%. After harvesting, nutrient elements were found to have bioaccumulated in plant organs (leaves, stem, and root) with the highest values being 29.7 mg/L for nitrogen in the leaf and this value was reported from the experiment with 50 kg N/ha. For phosphorus and potassium, the highest concentrations of 7.05 and 8.4 mg/L were recorded in the plant’ stem of the experiment with 50 kg N/ha. All the treated soils recorded an increase in values of all nutrient elements over the control with the highest values recorded in the experiment with 60 kg N/ha. In soil with 60 kg N/ha, the nitrogen, phosphorus, and potassium increased by 28, 40, and 22% respectively over the chemical fertilizer applied experiment while different levels of increases were also recorded for all other macro and microelements in all the experiments. Thus, agricultural practices by using anaerobic digestates as organic fertilizers is a sustainable method to overcome the dependence on inorganic fertilizers high rate.

Anaerobic co-digestion of bioplastics as a sustainable mode of waste management with improved energy production - A review

The world of bioplastics has expanded rapidly in recent decades, and the new waste stream generated is creating major barriers to waste processing. Anaerobic co-digestion is to be considered one of the best options for the efficient processing of bioplastic waste due to its minimal space requirements, lower degrees of environmental pollution, and renewable energy generation. The higher carbon to nitrogen (C/N) ratio of bioplastics poses a challenge to anaerobic digestion, but co-digestion with lower C/N ratio biowastes can efficiently degrade bioplastics and improve biogas production in the system. In the future, the collection of organic waste in biodegradable plastic bags makes the waste management process easier for anaerobic digestion plants. The present review paper discusses current trends of bioplastic usage, degradation strategies, and the potential of anaerobic co-digestion for waste management with improved energy production in anaerobic digesters.

Application of machine learning methods for the prediction of organic solid waste treatment and recycling processes: A review

Conventional treatment and recycling methods of organic solid waste contain inherent flaws, such as low efficiency, low accuracy, high cost, and potential environmental risks. In the past decade, machine learning has gradually attracted increasing attention in solving the complex problems of organic solid waste treatment. Although significant research has been carried out, there is a lack of a systematic review of the research findings in this field. This study sorts the research studies published between 2003 and 2020, summarizes the specific application fields, characteristics, and suitability of different machine learning models, and discusses the relevant application limitations and future prospects. It can be concluded that studies mostly focused on municipal solid waste management, followed by anaerobic digestion, thermal treatment, composting, and landfill. The most widely used model is the artificial neural network, which has been successfully applied to various complicated non-linear organic solid waste related problems.

Revalorization of bioactive compounds from tropical fruit by-products and industrial applications by means of sustainable approaches

Tropical fruits trade is on the rise due to the claimed health benefits related with their consumption. Functional activities are exerted by the presence of bioactive compounds which could be used for prevention or amelioration diseases. However, the occurrence of bioactive compounds is found mainly in non-edible fraction of tropical fruits which are usually discarded. Therefore, the revalorization of tropical fruits by-products as source of functional compounds is on the cutting-edge research. The implementation of this challenge not only allows the enhancement of the tropical fruits by-products management, but also the production of value-added products. This review compiles the latest comprehensive information about the revalorization of bioactive compounds from tropical fruits by-products. A revision of the sustainable green technologies used for the isolation of valuable compounds has been carried out as well as the current food, functional, cosmeceutical and bioenergetics industrial applications of bioactive compounds extracted from tropical fruits by-products.

Energy generation from anaerobic co-digestion of food waste, cow dung and piggery dung

The study investigated bioenergy generation from anaerobic co-digestion of food wastes (FW), cow dung (CD) and piggery dung (PD). The physicochemical parameters of the substrates were determined before and after digestion following standard procedures after mechanical pretreatment. Throughout the study, pH remained slightly alkaline while temperature varied between 26 and 32 °C. The highest cumulative biogas yield of 0.0488 L was recorded from the digestion of FW + CD + PD on the ninth day. After analyses, the highest methane content of 64.6 was obtained from the digestion of FW + PD while the lowest (54.0%) was from the digestion of FW only. Overall, cumulative biogas production for the four digestion regimes followed the order: FW + CD + PD, FW + PD, FW + CD and FW only respectively. Accumulation of VFAs was recorded at a slow rate during the digestions.

Co-digestion of Theobroma cacao (Cocoa) pod husk and poultry manure for energy generation: Effects of pretreatment methods

In this study, biogas was produced from the anaerobic co-digestion of Cocoa pod husk (CPH) and poultry manure. Pretreatment of the CPH was carried out using sulfuric acid and hydrogen peroxide. The physicochemical, elemental and structural analyses were carried out on the CPH before and after pretreatment. The microbial composition of the fermenting materials were also determined using standard method while the Fourier Transform Infra-red (FTIR) spectroscopy was used to identify the structural changes that took place after pretreatments. Use of alkaline hydrogen peroxide caused high solubilization of the lignin component of the CPH and reduced up to 81% of lignin i.e. initial value of 21.7% m.m^-1 to final value of 4.2% m.m^-1. Similarly, the alkali reduced the hemicellulose content of the CPH from 27.0% m.m^-1 to 8.5% m.m^-1. Overall, there was 68% increase in biogas volume from the alkaline pretreated CPH.

Data on energy and economic evaluation and microbial assessment of anaerobic co-digestion of fruit rind of Telfairia occidentalis (Fluted pumpkin) and poultry manure

The data described in this article was obtained in an experiment designed for the generation of biogas from the anaerobic co-digestion of Telfairia occidentalis (Fluted pumpkin) fruit rind and poultry manure both of which currently constitute an environmental nuisance in the localities where they are found. The data presented in this article is on the use of combined heat and power (CHP) system to assess the energy and economic feasibility of applying thermo-alkali pretreatment procedures to one of the substrates (Fluted pumpkin) prior to anaerobic digestion. Also, the microbial characterization and succession pattern of important microbes during the anaerobic digestion process was evaluated and the data reported in this paper.

Energy efficiency: Importance of indigenous microorganisms contained in the municipal solid wastes

2016 was an extraordinary year for renewable energy, as it had the largest global capacity additions seen to date. However, challenges remain, particularly beyond the power sector. Overcoming these challenges means pursuing goals on development and optimization of strategies focused in causing an increase in bioenergy usage. Considering the seriousness of the challenge this paper has been developed. In the present study, indigenous microorganisms gathered from municipal solid waste will be analysed at to find out the role such organisms have on an anaerobic digester and its performance, with the aim of producing biogas in order for it to be used as electricity or treated to produce high quality fuel. The presence of such anaerobic microbiota can help avoid the two most tragic situations of an anaerobic digestion plant: overloading and washing out. The information of the present paper would have to be considered in future researchers about pre-treatments because most novelty studies are focused on hard pre-treatment to destroy microorganisms in the substrate (to increase the biogas production). In the present paper, it is underlined that the destruction of the microbiota in the substrate could produce adverse effects in the performance in the reactor.

Experimental and feasibility assessment of biogas production by anaerobic digestion of fruit and vegetable waste from Joburg Market

Substrate-induced instability of anaerobic digestion from fruit and vegetable waste (FVW) results in low biogas yield. In this study, substrate management through fruit to vegetable mix ratio in a two-stage semi-continuous digester was investigated as a pathway for optimality of yield. The experiment conducted over 105 days with 62.52 kg of FVWs sourced from Joburg Market, South Africa showed that a stable process was achieved at a fruit to vegetable waste mix ratio of 2.2:2.8. At this ratio, optimal organic loading rate ranged between 2.68 and 2.97 kg VS/m³-d which resulted in a specific biogas yield of 0.87 Nm³/kg VS with 57.58% methane on average. The results of the experimental study were used as a feasibility assessment for a full-scale 45 tonnes/d plant for Joburg Market considering three energy pathways. The plant will produce 1,605,455 Nm³/y of biogas with the potential for offsetting 15.2% of the Joburg Market energy demand. Conversion of all biogas to biomethane was the most economically attractive energy pathway with a net present value of $2,428,021, an internal rate of return of 16.90% and a simple payback period of 6.17 years. This route avoided the greenhouse gas emission of 12,393 tonnes CO₂, eq. The study shows that the anaerobic digestion of FVWs as sole substrate is possible with financial and environmental attractiveness.

Seeking to enhance the bioenergy of municipal sludge: Effect of alkali pre-treatment and soluble organic matter supplementation

The aim of this research is to enhance the mesophilic anaerobic digestion of municipal sludge from Cadiz-San Fernando (Spain) wastewater treatment plant at 20days hydraulic retention time (HRT). Two different strategies were tested to improve the process: co-digestion with the addition of soluble organic matter (1% v/v); and alkali sludge pre-treatment (NaOH) prior to co-digestion with glycerine (1% v/v). Methane production (MP) was substantially enhanced (from 0.36±0.09 L CH₄ l/d to 0.85±0.16 L CH₄ l/d), as was specific methane production (SMP) (from 0.20±0.05 L CH₄/g VS to 0.49±0.09 L CH₄/g VS) when glycerine was added. The addition of glycerine does not seem to affect sludge stability, the quality of the effluent in terms of pH and organic matter content, i.e. volatile fatty acids (VFA), soluble organic matter and total volatile solid, or process stability (VFA/Alkalinity ratio<0.4). Alkali pre-treatment prior to co-digestion resulted in a high increase in soluble organic loading rates (more than 20%) and acidification yield (more than 50%). At 20days HRT, however, it led to overload of the system and total destabilization of the mesophilic anaerobic co-digestion of sewage sludge and glycerine.

Pretreatment optimization, process control, mass and energy balances and economics of anaerobic co-digestion of Arachis hypogaea (Peanut) hull and poultry manure

The study explored biogas production from the co-digestion of Arachis hypogaea hull and poultry droppings. Mechanical and thermo-alkaline pretreatments were applied to a sample of the mixture. Another sample was treated mechanically but without thermo-alkaline methods. Optimization was done using the Response Surface Methodology (RSM) and the Artificial Neural Networks (ANNs). The optimal values for each of the five major parameters optimized are Temperature of 32.00°C, pH of 7.62, Retention time of 30.00 day, Total solids of 12.00g/kg and Volatile solids of 10.00g/kg and the predicted biogas yield for RSM was 3903.1510^-3m³/kg TSfed and 3338.310^-3m³/kg TSfed for ANNs in the thermo-alkaline pretreated experiment. Gas chromatography show the CH₄ and CO₂ content of biogas generated to be 65.5±1.5%; 26±1% and 53±1%; 26±2% respectively. The co-digestion of peanut hull with poultry droppings and other energy-yielding substrates is further encouraged.

Synergy of Siam weed (Chromolaena odorata) and poultry manure for energy generation: Effects of pretreatment methods, modeling and process optimization

The co-digestion of Chromolaena odorata with poultry manure was evaluated in this study. Two samples of the weed: (A: which was pre-treated with mechanical, chemical and thermal methods) and (B: which was pretreated using mechanical and chemical methods only) were separately digested with poultry manure. Biogas generation started from the 2nd to 4th and 4th to 7th day for samples 'A' and 'B' respectively. The most desired actual biogas yield from samples 'A' and 'B' were 3884.20 and 2544.70 (10^-4m³/kg VS) respectively and the gas composition was 68±2% Methane and 20±2% Carbon dioxide for sample A while it was 62±3% Methane and 22±2% Carbon dioxide for sample B. In all, there was a 38.06% increase in gas generation in 'A' over 'B'. The coefficient of determination (R²) for the Response Surface Methodology (RSM) model (0.9009) was high suggesting high accuracy in the modeling and prediction. The worldwide usage of C. odorata is encouraged.

Study on optimization of process parameters for enhancing the multi-hydrolytic enzyme activity in garbage enzyme produced from preconsumer organic waste

The garbage enzymes produced from preconsumer organic waste containing multi hydrolytic enzyme activity which helps to solubilize the waste activated sludge. The continuous production of garbage enzyme and its scaling up process need a globe optimized condition. In present study the effect of fruit peel composition and sonication time on enzyme activity were investigated. Garbage enzyme produced from 6g pineapple peels: 4g citrus peels pre-treated with ultrasound for 20min shows higher hydrolytic enzymes activity. Simultaneously statistical optimization tools were used to model garbage enzyme production with higher activity of amylase, lipase and protease. The maximum activity of amylase, lipase and protease were predicted to be 56.409, 44.039, 74.990U/ml respectively at optimal conditions (pH (6), temperature (37°C), agitation (218 RPM) and fermentation duration (3days)). These optimized conditions can be successfully used for large scale production of garbage enzyme with higher hydrolytic enzyme activity.

Comparative biogas generation from fruit peels of fluted pumpkin (Telfairia occidentalis) and its optimization

This study evaluated the potentials of fluted pumpkin fruit peels for biogas generation using three different pre-treatment methods (A, B, C) and the optimization of its process parameters. The physic-chemical characteristics of the substrates revealed it to be rich in nutrients and mineral elements needed by microorganisms. Gas chromatography analysis revealed the gas composition to be within the range of 58.5±2.5% Methane and 27±3% Carbon dioxide for all the three digestions. The study revealed that combination of three pre-treatment methods enhanced enormous biogas yield from the digested substrates as against the use of two methods and no pre-treatment experiment. Optimization of the generated biogas data revealed that RSM predicted higher gas yield than ANN, the latter gives higher accuracy and efficiency than the former. It is advocated that fluted pumpkin fruit peels be used for energy generation especially in the locations of its abundance.