1. Introduction
Informal landfills refer to sites that use natural terrain conditions for waste treatment and are not constructed and operated in accordance with relevant national standards and norms [
1,
2]. They are characterized by unsophisticated construction, lack of environmental protection measures, and a high risk of environmental pollution. They are considered informal landfills because of the lack of a sound seepage control system and garbage leachate collection and treatment facilities. The leachate from the landfill sites poses a serious threat to the surrounding groundwater environment [
3], particularly for the high rainfall region of southern China, with its shallow groundwater level. Ammonia, chloride, heavy metal ions, and other organic compounds in leachate are released into the environment, and their toxicity makes leachate potentially hazardous to the environment [
4,
5,
6,
7].
Low-lying landfills form pools where waste is subject to long-term immersion, increasing the leaching efficiency of pollutants. Heavy seasonal rains and subsequent water flow causes surrounding surface water and soil environment pollution [
8,
9,
10].
Given the continuous updating of national environmental protection policies and the improvement of public environmental protection awareness during recent years, the governance of informal landfills has become an imperative environmental protection task [
11]. Because the construction, use, and operation of informal landfill sites differs from that of sanitary landfill sites, investigation before implementation of governance work and a targeted scheme design are particularly important [
12].
At present, China has accumulated a relative breadth of experience in the comprehensive treatment of informal landfills, but there is still a lack of systematic management ideas and complete technical schemes for informal landfills in rainy areas in southern China. The main reason for this is that for this type of landfill, during the process of treatment, in addition to considering the treatment and disposal of solid waste, there is also the problem of water environmental treatment as a result of rainfall. At the same time, the waste is degraded and converted to silt, which causes insufficient stability of its structure during the comprehensive treatment process and affects the implementation of the project. Silt pollutants result in questions of how to safely and effectively control or treat waste, which will influence the final determination of regulation schemes.
There are few reports regarding the treatment of water accumulated at informal landfills, but research regarding leachate in sanitary fields is quite mature and has achieved good results. Leachate contains a large number of harmful organic matters, heavy metals, and inorganic salts [
13]. There are many means to treat leachate, such as membrane bioreactors [
14] adsorption [
15], flocculation [
16,
17], and electrochemical methods [
18]. Advanced oxidation techniques are a good way to treat leachate, such as fenton, ozone, or other improved methods [
19,
20,
21,
22,
23,
24].
Treatment of leachate in general sanitary landfills is conducted in the field; however, this type of long process technology is not suitable for informal landfills. Leachate is treated only once, that is, after treatment, water is removed or connected to a municipal pipe network and no subsequent leachate is generated. At present, there is no effective integrated equipment to sufficiently treat leachate. Mature, low-cost, and high-efficiency leachate treatment technology is an effective means to solve the problem of water management at informal landfills. Regarding site investigations of informal landfills, most focus on the site risk assessment of the landfills, and those in arid areas of northern China are often taken as case studies [
25].
A survey of this type in the rainy areas in southern China has not been previously reported. Taking an informal landfill site in southern China as a typical case, this study aimed to (1) select the specific method of basic situation for the early stage of the government survey and investigation; (2) determine the main contents and key factors of comprehensive investigation of the environmental quality status; (3) explore a low-cost practical landfill technology to solve water pollution problem in site; and (4) summarize the processes of comprehensive treatment of the informal landfill site in a rainy area of southern China.
4. Conclusions
Through the investigation and analysis of the current situation of a typical informal landfill in southern China and the detection of the environmental quality of the site, the landfill stock and water volume were determined. The source and properties of incoming waste were determined, and the hydrogeological conditions, water quality, heavy metal content in the bottom mud, and extent of pollution were obtained. It was found that the number of indicators and pollutants exceeding the limits outside the site were far lower than those inside the site, indicating that the environmental quality of the off-site groundwater is less affected by the landfill leachate. However, if the water outside the site is also polluted, then the subsequent site treatment measures will increase the groundwater remediation. Adopting the treatment method of adding PAFC first and CH later results in higher clarity and lower color, better appearance of the treated water, and a faster removal rate of ammonia nitrogen. The sewage in the pond was treated to the standard and then connected to a downstream sewage plant for further treatment, thus solving the problem of sewage treatment. The project of backfilling guest soil and landfill covering fully achieved the comprehensive regulation of the landfill and reduced the risk of the site. The research and application of this project can provide a theoretical basis and practical experience for the comprehensive regulation of informal landfills in rainy areas in southern China.