Abstract
Autoclaving of food wastes (FW) for the resource recovery and reutilization was studied using the pilot plant scale. Experiments were conducted at various temperatures of 408, 428, and 438 K and times of 15 and 60 min. The in-filled steam to the autoclave was supplied by the incineration plant with a gauge pressure of 7 kg/cm2 and a temperature of 443 K or above. The results obtained from the experiments show that the less energy- and time-consuming autoclaving conditions (408 K and 15 min, denoted as Case A408-15) are effective. Comparisons of the properties and characteristics of autoclaved FW (FWA) of Case A408-15 with those of FW are made. The wet bulk volume and wet bulk density of FW A are dramatically reduced to 15.64% and increased to 313.37% relative to those of FW, respectively. This makes the subsequent processing and reuse for FWA more convenient than FW. The autoclaving results in an increase of carbon content and a decrease of nitrogen content, and thus an increase of the C/N ratio of FWA. The contents of sulfur, hemi-cellulose, and cellulose of FWA are also reduced. All these fluctuations are beneficial for making compost or other usages from FWA than FW. The autoclaved liquid product (LA) separated from FWA and liquid condensate (LC) from the released gas possess high COD and TOC. These two liquids can be mixed for use as liquid fertilizers with proper conditioning. Alternatively, further anaerobic digestion of the mixture of FWA, LA, and LC can offer enhanced biogas production for power generation. All these thus match the appeal of sustainable materials management and circular economy. The emitted gas from autoclaving contains no CO and some hydrocarbons. Suitable air pollution control is needed. The results and information obtained are useful for the proper recovery and reuse of abundant food wastes from domestic households and food industries.
Highlights
The autoclaving process is a mechanical heat treatment technique, which has been used to treat mixed industrial wastes, as well as municipal solid wastes (MSW), using saturated steam under high pressure
From the prospect of recovery and reutilization of food wastes (FW) by autoclaving pretreatment, the findings suggest that mild operation temperature and short operation time can conserve substantial energy needed in autoclaving of raw materials and effectively reduce the volume
The results showed that the lower energy level and operation time by autoclaving were achieved at 408 K and 15 min
Summary
The autoclaving process is a mechanical heat treatment technique, which has been used to treat mixed industrial wastes, as well as municipal solid wastes (MSW), using saturated steam under high pressure. Resource recycling takes advantage of the autoclaving process to reduce the volume of wastes and make them easy for sorting after solid-liquid separation. The valuable components of autoclaved solid products, such as the organic floc/fiber and inorganic recyclables (metal, plastics, and glass) can be obtained separately from other in-organic discards or rejects [1–10]. Autoclaving of bio-wastes can obtain solid organic floc/fiber without sorting the solid products, which contain little in-organics, if any; they are better than those from autoclaving of mixed wastes such as MSW and are more appropriate for use as RDF, SRF, or compost. Multiplication of T and t, i.e., T-t, which is proportional to the energy consumed, was adapted as a parameter to elucidate the performance at various T-t values
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