Drying Technology
Keywords: sludge dryer 、sewage treatment、sludge dryer
In today's increasingly scarce global water resources, the use of sewage treatment to achieve recycling is an important way to solve this problem. By analyzing the basic methods of sewage treatment and the introduction of the history and development status of sewage treatment in various countries in the world, this paper shows that recycling through sewage treatment is an economical and practical way to save energy for long-term development.
The significance of the development of renewable water resources
The current situation of water resources in the world and my country. Although 72% of the earth's surface is covered by water, freshwater resources only account for 0.75% of all . Nearly 70% of the freshwater is fixed in the ice layers of Antarctica and Greenland, and the rest is mostly soil moisture or deep groundwater, which cannot be used by humans. . Less than 1% of the fresh water on Earth, or about 0.007%, is directly available to humans. The global freshwater resources are not only in short supply but also extremely unbalanced in regional distribution. About 1.5 billion people in 80 countries and regions, which account for about 40% of the world's total population, have insufficient freshwater, and about 300 million people in 26 countries are extremely short of water. China is also a country with severe drought and water shortage. The total amount of freshwater resources is 2.8 trillion cubic meters, accounting for 6% of global water resources, ranking fourth in the world after Brazil, Russia and Canada, but only 2,200 cubic meters per capita, only 1/4 of the world average. , 1/5 of the United States, ranking 121 in the world, and one of the 13 countries with the poorest per capita water resources in the world. The amount of water resources available per capita is less, only 900 cubic meters, and the distribution is extremely uneven. By the end of the 20th century, among the more than 600 cities in the country, more than 400 cities had the problem of insufficient water supply, of which 110 cities had serious water shortages, and the total urban water shortage in the country was 6 billion cubic meters.
The development of renewable water resources is the general trend. The development and resources plays an important role in alleviating the shortage of water resources, promoting the rational use of water resources, and supporting sustainable social development. The combination of pollution reduction and environmental improvement is to solve the two major problems of urban water resources shortage and water environment pollution at the same time. The most economical and effective measure. Sewage discharge is stable and does not change with rainfall. Reclaimed water using sewage as water source can be used as a stable water supply source. The purified sewage can be used as a regenerated water resource with the characteristics of concentration, large quantity, stable water quality and quantity, and can be used for industrial, agricultural, municipal and building water use.
Status Quo of Reclaimed Water Development in Singapore
In order to solve the national water shortage problem, the Singapore government implements both open-source and cost-saving measures, and proposes the development of four major “national plumbing” plans, namely natural precipitation, imported water, new water and desalinated seawater. The Singapore NEWater Plan refers to the transfer of domestic sewage to the NEWater Plant through a reasonable drainage system, and after a series of treatments, recyclable NEWater is obtained. Most of the reclaimed water is supplied to industry, commerce, service industry, and landscaping, and a small part is injected into the reservoir, mixed with natural water, and sent to the waterworks. After further treatment, it reaches the drinking water standard and is indirectly used as drinking water. water supply. At present, the total daily supply of reclaimed water from its reclaimed water plant can reach 236,200 m3/d, accounting for more than 15% of the daily water supply, and the goal is to achieve more than 30% of the daily water supply. NEWater is Singapore's example of "turning the rot into the magical". With NEWater, Singapore is more self-sufficient in water supply, and the Chinese people also understand the importance of NEWater. Wastewater recycling, filtration, and regeneration, so that every drop of water can be used more than once.
The basic principle and process of
Membrane and ultraviolet disinfection technology are treated to become reclaimed water, and the cost of reclaimed water is S$0.3 per cubic meter of reclaimed water, which is far lower than the cost of desalination abroad.
Most plants still use the activated sludge process for wastewater treatment. All kinds of sewage are collected to the sewage treatment plant through pipelines. First, there must be a grille for preliminary cleaning to intercept large-scale sewage. In order to raise the upstream water to the height required for the subsequent process, the pump room is required to pump the water to the primary sedimentation tank. The primary sedimentation tank and the secondary sedimentation tank are an important part of the sewage treatment process. The primary settling tank removes about 50% of the sediment, grease and floating matter by sedimentation. The sewage then enters the aeration tank, and the aeration tank conducts sewage treatment through the principle of aeration. It is also an important step in the activated sludge process. Aeration is a means of intense contact between air and water, and its purpose is to dissolve the oxygen in the air into the water, or to expel the unwanted gases and volatile substances from the water into the air. In other words, it is a means of facilitating the exchange of substances between gases and liquids. In the aeration tank, air is continuously introduced into the wastewater, and after a certain period of time, sludge-like flocs are formed due to the reproduction of aerobic microorganisms. It is inhabited by microbial groups dominated by bacterial micelles, which have a strong ability to adsorb and oxidize organic matter. Adsorbs the dirt in the water to the sludge. The water then enters the secondary sedimentation tank, which is an important part of the activated sludge system, and its function is to separate the sludge, clarify, concentrate and return the activated sludge to the mixed liquid. Its working effect can directly affect the effluent quality and return sludge concentration of the activated Part of the sludge settled in the secondary sedimentation tank will be returned to the aeration tank to continue sewage treatment. Some of the treated sewage is poured into groundwater, and some is used as reclaimed water for daily activities such as car washing.
4. Status Quo of Sewage Treatment Development in Other Countries
United States: The United States has used reclaimed water as a water supply resource for 20 years, and can be described as a pioneer in reclaimed water. As early as 1976, the 21st Century Reclaimed Water Plant in Orange City Water District, Southern California, USA, the high-quality reclaimed water extracted by membrane technology was injected into the surface water. [Excerpted from "Water Supply and Drainage Technology Trends", No. 02, 2004. The technical level and development trend of the United States and Singapore using membrane technology to achieve sewage recycling and reuse Author: Li Jian; Li Fuyuan. ] Now the largest wastewater treatment plant in the United States, the ELWRF, was built in El Segundo, Los Angeles County, in 1992. The water treatment plant produces 30 million gallons of reclaimed water per day, saving enough water to last 60,000 homes for a year. This number is staggering and shows the importance of water regeneration. Reclaimed water can be used for many purposes, ELWRF is the only treatment plant in the United States that can produce 5 different waters according to customer requirements. The five types of water are: 1. tertiary water widely used in industrial and agricultural irrigation; 2. nitrified water used in industrial cooling towers; 3. softened reverse osmosis water: the secondary treated water is microfiltered, reverse Osmosis and disinfection, and then replenished back to groundwater; 4. Purified reverse osmosis water, used in low pressure boilers in refineries; 5. Ultra-high purity reverse osmosis water, used in high pressure boilers in refineries. More types of reclaimed water can make full use of these hard-won water resources. In the U.S., even water reclamation plants are saving to the end. ELWRF has installed 60,000 square feet of solar energy, which can provide 10% of the water treatment plant's peak electricity consumption. The application of this solar energy reduces 356 tons of carbon dioxide emissions to the atmosphere each year, equivalent to Yu planted 100 acres of woods, or drove 890,000 fewer miles. [Excerpted from the Sino-US Environmental Technology Exchange Forum "The Largest Reclaimed Water Treatment Plant in the United States - Los Angeles West Bay ELWRF"] The environmental protection spirit of the American reclaimed water plant is worth learning from all countries, and it is more economical in saving.
