Food waste pretreatment process
Food waste is transported to treatment plant by transport vehicles, weighed by weighbridges and recoded in standing book. Food waste is poured in receiving hopper whose bottom is equipped with a three screw feeder because there are lots of water and impurities in food waste. The bottom plate of hopper is of porous structure, and a leachate collection pool is arranged at the bottom of the receiving hopper, which is used to collect organic slurry leached during transportation, and then it is pumped to the inert separation device.
Food waste in receiving hopper is lifted by the screw conveyor into the automatic sorter. Main function of the automatic sorter is to separate the plastic, fabric, hard and non-fragile inorganic materials such as metal and other sundries in food waste. At the same time, food residue in food waste is pulped to produce organic crude slurry. Solid organic matter (food, bone, wood and bamboo, etc.) and easy-broken matter (shell, glass, porcelain, etc.) are broken and discharged by rotary hammer in the automatic sorter, while light matter (plastic, fabric, etc.) and metal which are not easy to break are not completely crushed due to the special design of rotary hammer, and they are transported to post stage and discharged.
Food waste material forms slurry after automatic separation and pulping, material is sent to slurry heating device by slurry delivery pump. There are mainly two functions of slurry heating process: firstly, it is beneficial to maximize efficient of oil recovery process; secondly, solid organic matter in the crude material can be maximally separated via action of high temperature and agitation and enter liquid phase in next process. Heated material enters solid-liquid separator for separation of two phases, part of solid organic matter will also dissolve into the liquid phase during separation. Organic slurry and the leached liquid are combined into the inert separation device to remove gravel and scum, and then enter oil recovery and purification unit. Gravel and scum are transported out for disposal. Solid phase is sent to biological hydrolysis reactor.
After the scum and grit are removed, slurry firstly enters the three-phase oil extractor to separate grease, solid slag and organic slurry. The purity of the crude oil can reach over 97%. The mixed slurry is pumped into the anaerobic reactor.
Kitchen waste pre-treatment process
After entering treatment plant, kitchen waste is discharged inti receiving hopper and lifted by chain conveyor to bag-breaking drum screen. Drum screen is provided with 1200mm-screen, screen residue is mainly plastic, fabric and other high calorific value combustibles, which will be transported out for incineration. Undersized material is mainly organic material and the rest includes paper, plastic, inorganic inert materials and other sundries, these material enter the biological hydrolysis reactor after Magnetic Separation.
Co-biological treatment process
Solid-phase material from food waste pre-treatment separation unit and screen residue from kitchen waste pretreatment is sent to biological hydrolysis system for co-processing. Most biodegradable organic matter remained in the materials entering the biological hydrolysis reactor, which was transformed from solid phase to liquid phase via biological hydrolysis action and mechanical agitation. Solid phase and high concentration organic slurry are produced by extrusion dehydration of biological hydrolytic effluent. Moisture content of the solid phase is about 55%, and it is incinerated. The organic slurry enters the slurry pretreatment unit to remove the residue, sediment and scum.
Organic slurry from food waste and kitchen waste pretreatment unit is combined and sent to anaerobic digestion system, biogas generated from anaerobic system can be applied for resource utilization. Screen residue, extrusion dehydration solid residue and anaerobic biogas digestate can be incinerated together. Part of biogas slurry is returned to biological hydrolysis reactor as spray water, and the rest of biogas slurry is sent to wastewater treatment system.
Food waste treatment process is reliable, operation of core equipment is stable, large-particle inorganic phase can be avoided entering anaerobic digestion system by pretreatment process. This process has been applied in more than 30 projects.
EMBT process is applied for kitchen waste treatment, advantages are as follows:
① High adaptability of waste with different classification efficiency.
②Good reduction performance. Biological hydrolysis technology can convert bound water into free water and realize separation of easy degradable organic matter and combustibles, this is helpful to utilization. COD of organic liquid phase is 60000-80000 mg/L, moisture content of extruded solid phase is about 55%. Lower calorific value is increased from 200 kcal/kg ( raw kitchen waste) to 1600-2000 kcal/kg (solid phase discharge).
③The process can increase capacity of waste incineration plant, improve efficiency of waste power generation, stabilize combustion conditions, and realize high efficient of energy utilization.
④There is no need of digestate treatment compared with other process, which also means lower processing cost and less environmental impact.
⑤Process is simple, stable and has been successfully applied for more than ten years.
Advantages of co-process of kitchen waste and food waste
①Co-process of solid phase: organic solid phase with impurities from food waste treatment pretreatment unit enters biological hydrolysis reactor for co-process, organic matter is recycled into liquid phase by hydrolytic acidification, in which way resource recovery can be promoted.
②Co-process of liquid phase: liquid phase from kitchen waste and food waste pretreatment unit enters anaerobic system for co-process. Impact load from different features of liquid phases can be alleviated via water quality regulation, it is helpful to stable operation of anaerobic system. High-temperature slurry of food waste and medium-temperature slurry of hydrolysis reaction is mixed for mesophilic anaerobic, waste heat is used and operation energy consumption can be reduced.