Bioconversion of Organic Wastes from Fruit and Vegetable Market

Vegetable and fruit waste is a biodegradable material generated in large quantities, much of which is dumped on land to rot in the open, which not only emits a foul odor, but also creates a big nuisance by attracting birds, rats, and pigs - vectors of various diseases. Apart from post-harvest losses due to lack of storage capacity, processing, and packaging of vegetables according to customers’ specifications also plays a major role in waste generation. Vegetable and fruit wastes include the rotten, peels, shells, and scraped portions of vegetables and fruit or slurries. These wastes can be treated for biofuel production through fermentation under controlled conditions, or else used for composting. The natural decomposition of wastes by microbes generates products with high humus content. Research activities have confirmed that this carbohydrate-rich biomass can be a potent substrate for renewable energy generation (Singh et al. 2018, 2017a, b, c, 2019; Tiwari et al. 2018, 2019a, b; Kour et al. 2019). A huge amount of vegetable and fruit waste is generated on a daily basis from diverse sectors such as vegetable markets, agro-based companies, hostels, hotels, restaurants, canteens, hospitals, housing societies, institutions, waste dumping yards, etc.

Characterization of Vegetable and Fruit Wastes

Vegetable and fruit wastes are a special group of biomass that needs to be characterized to understand its nature for application as raw material and to propose the best methodology for its proper utilization. Waste composition also influences the overall yield and kinetics of the biologic reaction during digestion. Characterization of waste can be done physically, chemically, or biologically. Physical characterization of solid wastes include estimation of weight, volume, moisture, ash, total solid, volatile solid (VS), color, odor, temperature, etc., while dissolved and suspended solids are estimated for liquid wastes. Turbidity is another important parameter for liquid wastes, which needs to be considered. Chemical studies include the measurement of cellulose, hemicellulose, starch, reducing sugars, protein, total organic carbon, phosphorus, nitrogen, BOD, COD, pH, halogens, toxic metals, etc. Besides these biochemical parameters, carbon, phosphorous, potassium, sulfur, calcium, magnesium, etc. can also be tested. All these chemical and biochemical parameters provide an insight into the applicability of waste for employment in fertilizer production. Biological characterization indicates the presence of pathogens and organisms which are indicators of pollution. A common feature of various forms of food wastes includes high COD, richness in protein, carbohydrate, and lipid biomolecules with noticeable pH variation. It has been reported that wastes from vegetable industries (including carrots, peas, and tomatoes) have a high BOD and are a rich source of several nutrients like vitamins, minerals, fibers, etc. So, a detailed study of waste characteristics is essential for deciding its application and determination of the economic feasibility of the process.

Management of Vegetable and Fruit Waste

There are seven commonly used methods of managing fruit and vegetable waste. The list of methods provided here will define the method of management. This list cannot be easily arranged in order of best management practice from an environmental standpoint due to the individual circumstances of the farmer and the packing house where culls originate. The management options are provided as a means to help better explain how each may be used. The seven management methods are:

  • 1) Store the culled fruit and vegetables on-site in a pile or bermed area for a limited time
  • 2) Return fruit and vegetable waste to the field on which it was grown
  • 3) Feed fruit and vegetable waste to livestock
  • 4) Give the fruit and vegetable culls to local food banks
  • 5) Compost fruit and vegetable culls
  • 6) Process fruit and vegetable culls to separate juice from pulp
  • 7) Dispose of fruit and vegetable waste in a local Sub-Title D landfill

Store the Culled Fruit and Vegetables On-Site

Storing culled fruit and vegetable waste on-site is a temporary solution to final disposal or the reuse of materials. To use this method, the culls may be hauled or transferred via mechanical methods to a location that has been prepared for holding the culls. At a minimum, the holding area should be bermed to capture and hold rainfall and any liquids that have formed from the decomposition of the culled fruit and vegetables. Other options for such a site include storage in tanks or bunkers with easy access for moving liquids or solids for later management. The culls stored in the bermed area should be crushed, if possible, to allow available liquid to better evaporate. Crushing the culled fruit and vegetables and placing them in a bermed area helps control the leachate, run-on and runoff, makes managing the material easier, allows extra liquids to evaporate, and reduces the volume that will need to be managed at a later time.

Return Fruit and Vegetable Waste to the Field

From an agricultural nutrient management and organic building viewpoint, returning fruit and vegetable waste to the field may be one of the better options. This management method returns the culls back to the growing field where the nutrients can be recycled, allowing the fruit and vegetable pulp and juice to help build or maintain the soil organic matter content. The cost can be very low, based on the distance to the field and the amount of liquid removed. The protocol for transporting the culls to a growing field will consist of storing the culls at the packing house or at the field site until final harvesting of the crop. After the final harvest, the culls or remaining solids and liquids can be loaded into spreader trucks and applied evenly across the field. As a matter of practice, the material should be incorporated, which will reduce the potential for problematic odors and runoff.

Feed Fruit and Vegetable Waste to Livestock

Managing culls by feeding fruit and vegetable waste to livestock may be a good option based on the overall management system of the livestock operation. One of the major issues that must be addressed involves the nutritional benefits and effects of feeding culls to livestock. Farmers should consult with animal scientists or veterinarians to confirm the effects of feeding culls to livestock.

Give Good Fruit and Vegetable Culls to Local Foodbanks

Food banks may be an option to manage some of the culls resulting from the sorting of the fruit and vegetables. Giving culls to a food bank may be an option and the Good Samaritan Law will protect the donating company. However, since fruit and vegetables are perishable, not all of the culls can be utilized by this method. The farmer should stay in contact with the local food bank coordinator to inform them of harvest dates and what may be available, as well as to determine whether anyone would be allowed in the packing house and whether bins of culls would be available for further off-site culling and packaging for distribution to other food banks. The coordinator would need to provide a means to safely transport the culls to a location for further processing, if needed, and the remaining culls would have to be disposed of using another method listed in this document.

Compost Fruit and Vegetable Culls

Composting culled fruits and vegetables is one option that can reduce the volume of culls as well as other “waste” materials in a community, if the land and equipment are available. Culls used in the compost process would either be transferred in a truck to the composting facility or mechanically transported if the compost facility is on-site. The culls would be mixed in proper ratios with other organic materials as recommended by composting professionals to produce compost suitable for incorporation into fields or for selling.

Process Fruit and Vegetable Culls to Separate Juice from Pulp

The method of separating the fruit and vegetable culls into juice and pulp is accomplished by using a press. Typical systems are screw' presses that can effectively separate the juice from the pulp. After separation, each fraction has its benefits for different reasons and purposes. If the culls are of good food quality they can be used as juices in food applications based on available markets. The pulp can also potentially be used as a component of foods. For those culls that are not of human food quality, the separated pulp can be used as one component of compost or animal food. (If the pulp is used for animal feed, check with an animal scientist or veterinarian prior to feeding.) The pulp can also be used as a soil amendment or as one component of a composting process. The juice can also be used as a feedstock for ethanol production or anaerobic digestion processes. For either process, there should be a market for the final products: ethanol or methane.

Disposal of Fruit and Vegetable Waste in Landfill

Disposal of culled fruit and vegetable waste in landfill is a method that should be considered after all other options. From a sustainability standpoint, disposal of these culls in a landfill is probability not the best option based on fees. If landfilling is the chosen option, management of the culls should reduce leakage of liquids from the transport truck.

Management of Fruit and Vegetable Waste for a Specific Packing House

The above methods for the disposal or reuse of fruit and vegetable waste are provided for all fruit and vegetable packing houses. The disposal method specific for any given packing house may be different and must be a decision based upon the particular location and situation. There may be more disposal methods available to specific packing houses. Individual packing houses will have to identify additional pros and cons and take them into account. This document is provided only as a guide to aid the individual packing house in identifying different options that may be suitable for disposing of culled fruits and vegetables.

The collected organic materials can be shredded, weighed in specific ratios, layered in mud pots, and kept in anaerobic conditions for pre-digestion. After a predecided duration, earthworms are introduced for further decomposition in semi- aerobic conditions. Moisture content is maintained by the sprinkling of water and periodical mixing (Table 6.1).

The compost sample was analyzed for nitrogen (micro- Kjeldahl method, Humphries 1956), phosphorous (Colorimetric method, Jackson 1973), potassium (Piper 1966), and micronutrients, (zinc, iron, manganese, and copper) following the method of Jackson (1973) (Table 6.2).

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