Difficulties and priorities in the treatment of kitchen waste leachate!

Kitchen waste accounts for a significant proportion of our household waste, but it also has dual characteristics of harmfulness and resource coexistence. Therefore, two opinions have emerged: one is to thoroughly clean up kitchen waste to avoid environmental harm, and the other is to start from its advantages, disadvantages, and current situation, and develop new technologies. Today, I will share with you the difficulties and key points of treating kitchen waste leachate!

Kitchen waste leachate

Kitchen waste generates a large amount of pollutants during transportation and accumulation, such as ammonia and hydrogen sulfide. These substances will directly dissolve in the leachate of kitchen waste, becoming the main problem of treatment.

Since the country vigorously promoted garbage classification in 2019, various regions across the country have formed three-year plans to implement garbage classification locally. After garbage classification, it will inevitably have a significant impact on the water quality of leachate. The amount and quality of leachate from landfills and waste incineration power plants will have a significant impact. Relatively speaking, there are many mature cases of these two types of leachate, and they will be improved and adjusted based on the original foundation.

The leachate from kitchen waste after garbage classification has become a hot topic of concern at present. The on-site treatment of kitchen waste (wet waste) after the distribution of garbage has ushered in a "spring" and is currently showing an explosive trend. At the same time as the outbreak, one of the environmental protection issues that restrict the promotion of the on-site treatment system is the standard discharge of leachate (sewage) treatment.

To consider how to meet the standards for the leachate (sewage) of kitchen waste, let's first understand the composition of kitchen waste, analyze the water quantity and quality of the leachate (sewage) from the moisture content of kitchen waste, and design accordingly.

On July 17, 2020, an analysis of the composition and properties of terminal household waste in Guangzhou in 2019 was posted on the official website.

According to the analysis, the physical composition (weight percentage) of household waste in Guangzhou in 2019 is as follows: kitchen waste (mainly organic perishable waste) 55.04%, rubber and plastic 23.03%, textile 8.66%, paper 6.99%, glass 2.22%, wood and bamboo 1.64%, mixed 0.93%, brick and tile ceramic 0.80%, metal 0.68%, and others 0.01% (among which, "mixed" refers to mixtures with particle sizes less than 10mm that are difficult to classify; "other" refers to waste batteries and other substances). The main properties of household waste are as follows: bulk density of 266kg/m3, moisture content of 54.54%, and low calorific value on a wet basis of 6869kJ/kg.

Specifically, regarding kitchen waste, according to the analysis of relevant papers, it can be seen that the average moisture content of kitchen waste components is as high as 79.5%. The main dry basis components are food waste and bone shellfish, with high total oil content and abundant nutrients. Solid waste accounts for about 18% of kitchen waste, waste oil accounts for about 3%, and kitchen wastewater accounts for about 79%; Solid kitchen waste mainly contains starch, crude protein, and crude fat, accounting for 32%, 20%, and 29% of the total mass, respectively.

According to the paper "Analysis of Physical and Chemical Characteristics of Household Kitchen Waste after Classification in Shanghai"

A comprehensive test was conducted on the physical and chemical characteristics of kitchen waste in the selected 6 streets. The test results showed that the moisture content of kitchen waste in Shanghai was between 73% and 89%, the C/N ratio was between 14 and 20%, the fat content was between 0.7% and 2.1%, the protein content was between 1.25% and 2.15%, and the salt content was between 0.09% and 0.29%. The heavy metal content was all below the limit standards of the "Limits for Pollutants in Food" (GB2762-2012).

Du Yu, a professor level senior engineer and senior expert in leachate treatment at the North China Design and Research Institute of Municipal Engineering in China, once mentioned in a live broadcast in May 2020 that most of the leachate from kitchen waste follows the third level standard, but the requirements for total nitrogen are relatively strict. Moreover, kitchen waste treatment plants cannot absorb concentrated liquids, so the non membrane method will have more application prospects in kitchen waste leachate.

If anaerobic fermentation is used to treat kitchen waste, due to the ammonification process that occurs during anaerobic fermentation, the ammonia nitrogen content in the biogas slurry is very high (the measured value of the built project is as high as 4000mg/l). Applying it to the treatment of leachate from kitchen waste due to the high total nitrogen content in the influent will be a consideration for denitrification throughout the entire process, rather than relying on a single point.

The complete denitrification of kitchen waste leachate and the process without concentrated solution will be a process technology that meets the needs of society, and is also a difficult and key point for kitchen waste leachate.