International Journal of Recycling of Organic Waste in Agriculture
Volume:7 Issue: 4, Autumn 2018

Waste management is one of the significant challenges facing Nigeria’s agricultural sector. To manage this problem, the conversion of agricultural wastes to biochar is a practical solution. In this work, the chemical composition of biochar from rice husk and sugarcane bagasse, two predominant agricultural wastes, commonly generated in Nigeria was studied. These wastes were pyrolyzed at 300–700 and 350–700 °C for rice husk biochar (RHB) and sugarcane bagasse biochar (SBB), respectively. It was found that biochar yield and total nitrogen decreased with increasing pyrolysis temperature while ash content, pH, EC, total carbon, extractable Ca, Mg, Na, available phosphorus and silica were increased. In RHB, extractable K increased with increasing pyrolysis temperature, while in SBB it decreased with its maximum observed in RHB. Rice husk pyrolyzed at high temperature may produce nutrient-rich biochar with high nutrient contents and these could ameliorate acidic soils. Finally, SBB could give high available silicon with acid pre-treatment.

Stevia rebaudiana residues composting is studied and optimized using a central composite experimental design The influence of controllable composting variables [moisture (40–70%), aeration (0.05–0.30 Lair min−1 kg−1), and time (0–50 days)] on the temperature history and the properties of the compost (pH, organic matter) produced to determine suitable composting conditions. Mass balance and emitted gases of all the composting reactors have been done. Compost with high degradation entails operating at 50 days of composting under high moisture content (70%) and aeration level with values close to 0.05 Lair min−1 kg−1. Moreover, the composting process kinetic for Stevia rebaudiana residues has been studied. The magnitude of the kinetic parameters on the studied conditions varies among 1/42 and 1/46 for 1/K1 and 0.15 and 1.6 for K2. Where 1/K1 is a value that measures the affinity between microorganisms and substrate and K2 depends on the composting variable optimization. Both moisture and aeration affects positively and negatively the composting process. Moreover, low effect of aeration has been found. The values of 1/K1 and K2 obtained showed higher values (higher degradation kinetic) under 55% moisture content and 0.30 Lair min−1 kg−1.

The study evaluated dried manures and manure ashes as alternative products from animal manures, and determined the dynamics of soil nitrogen availability indices and organic carbon release in some soils amended with dried manures and ashes under laboratory incubation, screen-house and field experiments. Cattle, goat and poultry manures were collected and air dried to produce dried manures after which part of the dried manures were burnt in open space at a temperature range of 320–450 °C to produce manure ashes. Treatments which were no amendment (control), dried manures of cattle, goat and poultry manure ashes of cattle, goat and poultry and NPK 15-15-15 at 120 kg N ha−1 were applied to soil. Samples were taken fortnightly after amendment incorporation in the incubation experiment; in screen-house experiment and field experiments, plant seeds were established after amendment incorporation; thereafter, soil samples were taken fortnightly. Soil samples were analyzed for soil organic carbon (SOC), NH4+–N and NO3−–N using a spectrophotometer. Incineration of manures increased pH, exchangeable cations and carbon, while nitrogen in manures ashes was comparable to nitrogen in dried manures. The application of manure ash increased SOC, NH4+–N and NO3−–N by 182, 102, 128% in incubation experiment while 64 and 628% increase in SOC and NH4+–N was recorded in screen-house experiment, respectively, relative to the control. In the field experiment, a significant increase in NO3−–N was recorded at the onset of incorporation; nitrification was more pronounced than ammonification under incubation and field conditions. Dried manures are not superior to manure ashes and incorporation of manures ashes increased the SOC, NH4+–N and NO3−–N though changes with increasing weeks were erratic.

In soil-based nursery media, topsoil, poultry droppings and sawdust conventionally provide anchorage, nutrients and aeration, respectively. Considering poultry droppings’ scarcity and sawdust’s inertness nutrient-wise, more readily available organic wastes should be explored as substitutes. Here, we evaluated the effect of such substitution on media fertility, aimed at seeking alternatives to the conventional practice. In a topsoil-manure-aerator volume ratio of 3:2:1, poultry droppings was substituted with pig slurry (slurry) or cattle dung (dung) as manure and sawdust with rice-husk dust (huskdust) as aerator, giving seven soil-based media including reference medium (topsoil+droppings+sawdust) and the control (topsoil+topsoil+topsoil). They were watered regularly and analysed for fertility parameters 4 months later. Reference had the highest pH (8.60) and topsoil + dung + huskdust/control the lowest (6.83). Substituting sawdust with huskdust enhanced pH, organic matter and Mg2+ in droppings/dung-amended media (topsoil+droppings+huskdust/topsoil+dung+huskdust) unlike slurry-amended ones where it too reduced total nitrogen (0.19 vs 0.11%). The substitution also enhanced available phosphorus in topsoil+droppings+huskdust (117.50 mg kg−1) and topsoil+dung+huskdust (71.50 mg kg−1) but reduced K+ in the latter where it too had moderating effects on Na+. Reference surpassed topsoil+slurry+huskdust for Ca2+, but was surpassed by topsoil+droppings+huskdust for Mg2+. Reference/topsoil+droppings+huskdust and topsoil+slurry+huskdust/control showed highest and lowest CEC, respectively. Excluding pH, topsoil+dung+huskdust and topsoil+slurry+sawdust were, notably, consistently similar. Overall, droppings-amended > dung-amended > slurry-amended media and, for available phosphorus only, sawdust-aerated < huskdust-aerated media. Based on fertility status 4 months after blending, topsoil+droppings+huskdust could serve as alternative to the conventional nursery medium, or topsoil+dung+huskdust where near-neutral pH is preferred to increased phosphorus/cations release.

In this study, vermicomposted tannery wastes were applied in the organic cultivation of sweet pepper in a greenhouse. The effects of this organic matter addition on plant development and on the distributions of Cr(III) and Cr(VI) in plant tissues and organs were assessed. In a greenhouse, organic sweet peppers were cultivated adding vermicomposted tannery to the substrate (sample VRC) and the results were compared with the samples control (dYL; only soil) and reference (NPK; adding mineral fertilizer). The growth, nutritive value and fruit production were assessed to evaluate the plant development in different types of substrate. Besides evaluating the biostimulant effect of vermicomposts, the distributions of Cr in plant tissues were also studied. Up to three harvested sweet peppers were obtained per plant, compared with only one fruit for the reference treatment with NPK addition. Based on the Cr dynamics in the plants, the highest concentration was found in the fruits, varied as follows: fruits > stem and stalks > leaves = root; however, the Cr concentration in the fruits was statistically the same across all treatments. Additionally, only Cr(III) was detected and quantified in the fruits. The addition of vermicompost was biostimulating to plants and positively influenced their development. Based on the Cr dynamics in the plants, since the Cr concentration was the same across all treatments, it demonstrated that the addition of tannery residues to the vermicompost did not negatively influence the health benefits or food security of the produced fruits.

Membrane filtration is recently applied to recover nutrients and dischargeable water from anaerobic sludge. The purpose of this study is to quantify nutrient separation, membrane performance, and process stability and to increase the economical applicability of the process by energetic optimisation. At the site of a 2.5 MWe agricultural biogas plant, a membrane pilot plant was operated over a period of 7 months. It consisted of a screw press separator, a decanter centrifuge, an ultrafiltration unit, and a three-stage reverse osmosis unit. Mass and nutrient balances were generated by sampling and analysing every process stream. Process performance was analysed by monitoring separation efficiencies, membrane flux, cleaning intervals, and energy demand. Solid/liquid separation resulted in separation efficiencies of 70% for total solids and 80% for phosphorus. The solid fraction contained high concentrations of organics and particle-ligated nutrients (20% TS, 8 kg t−1 Ntotal, 5.5 kg t−1 P2O5). The retentate of the reverse osmosis had high concentrations of dissolved ammonia and potassium (4 kg t−1 NH4–N and 10 kg t−1 K2O). 38% of the sludge volume was recovered as clean water. The membrane pilot plant successfully produced a solid N/P-fertiliser, a liquid N/K-fertiliser and clean water. The results contribute to a sound understanding and growing database for future adaption of the process chain. Hydrodynamic optimisation within the pilot plant reduced the energy demand of the ultrafiltration step by 50%, which considerably contributes to the economy of the process.

This study aimed to investigate the effect of time interval between sowing and amendment with non-digested and digested poultry manure and their combinations with urea on the germination of three wheat cultivars (Slambo, Acsad, and Karim) in the desert soil. The cultivars were sown on four different dates, i.e. directly, 10, 20 and 30 days after amendment. Fertilizers were applied at a rate of 350 kg Tot N ha−1. The germinated seeds were recorded daily starting at day 4 after sowing until day 14 after which the following germination attributes were calculated: time to reach 50% germination (T50%), final germination percentage (FGP) and germination index (GI). Additionally, radicle length, plumule length and seedling dry weight were also determined. Sowing near to the application delayed and reduced seeds germination particularly in the treatments amended with non-digested and digested manure in combination urea. This was confirmed by all germination attributes, i.e. high values of T50% and low values of FGP and GI. Moreover, sowing near to the application reduced the length of plumule and radicle as well as decreased seedling dry weight of all wheat cultivars. Results suggested that prolonging the period between amendments and sowing to 20 or 30 days would give better germination attributes and increase plumule and radicle length plus increasing seedling dry weight.

Wheat straw is an agricultural waste which can be used as a cost effective animal feed. However, high hemicellulose and phytic acid content in wheat straw prevents it as a primary feed choice. Utilization of wheat straw in solid-state fermentation may result in wheat straw valorization and enzyme production. In this study, phytase production in solid-state fermentation of wheat straw using Aspergillus ficuum and valorization of wheat straw were evaluated. A two-step experimental design procedure was employed for screening and optimization of influencing factors on phytase production. Effects of different nutritional and environmental factors were investigated by one factor at the time method (OFATM). To reach higher amounts of phytase, response surface methodology (RSM) was employed to optimize phytase production as a function of three of the most effective factors. Optimization of the significant parameters resulted in an increase in the phytase activity from 0.74 ± 0.12 to a maximum of 16.46 ± 0.56 Units per gram dry substrate (U gds−1). The high degree of the fungal phytase activity on wheat straw resulted in the decrease in phytic acid content by 57.4%, as compared to the untreated sample. Scanning electron microscopy (SEM) and FTIR structural analysis showed intensive fungal growth on wheat straw, and partial removal of hemicelluloses, lignin and phytic acid. The study demonstrated the feasibility of wheat straw utilization in solid-state fermentation using Aspergillus ficuum toward the production of phytase and valorization of wheat straw as an animal feed.

Peat-based substrates constitute the preferred media in conventional and organic nursery production. Nevertheless, in recent years, there has been a growing interest in environmental impacts associated with peat extraction that has increased with the demand of these non-renewable substrates. The re-use of organic wastes as substrate seems to be good solution to substitute commercial peat. This study evaluates date-palm peat (wastes of date-palm branches base locally known as “Kornef”) as an alternative nursery substrate. The research was conducted in a completely block randomized design with a linear substitution (0, 25, 50, 75 and 100%) of peat with date-palm waste peat for transplant production of lettuce (Lactuca sativa L.). Different physicochemical parameters (porosity, bulk density, pH, and CEC) of cultivation substrates were measured. The growth parameters (leaves number, leaves area, length, chlorophyll values, fresh and dry weight of seedlings) were evaluated at the end of growth period (when the seedling reached the commercial transplanting size). The results showed that date-palm waste peat is an appropriate media for nursery production, showing similar properties with commercial peat and best plant response with 25 and 50% substitution. In view of low cost, availability and large area of date-palm cultivation in Tunisia and over the world, it seems that peat can be replaced with substrate of date-palm wastes in the horticulture sector.

Different agricultural substrates were evaluated for growth and productivity of cucumber under pot culture for kitchen gardening. Several agricultural substrates such as leaf compost, compost, perlite, and coconut compost were used in with silt in several combinations. Seeds were sown in plastic pots of 9-L capacity and filled with growing substrates in various combinations. The study consisted of eight treatments; each treatment had four replicates. Use of different growing media alone or in combination significantly enhanced plant growth and productivity, compared to control. Results showed that maximum germination, plant growth, emergence percentage, gas exchange attributes, shoot/root length, shoot fresh and dry biomass, root fresh and dry biomass, no. of leaves, leaf mineral contents, and chlorophyll concentration and yield was noted in the plants grown in leaf compost + perlite + silt (1:1:1) media combination. In case of proline contents, all treatment combinations showed non-significant; but, NPK status varied because of the presence of organic matter in substrates that ultimately enhanced the nutrient uptake of cucumber plants. Although all media either alone or in combination positively influenced different studied parameters of cucumber, but, leaf compost + perlite + silt (1:1:1) combination was the best. Therefore, leaf compost + perlite + silt (1:1:1) media combination could be considered suitable for the cucumber cultivation in the form of kitchen gardening.