Municipal sludge treatment and disposal technology
DATE：2016-10-27
With the development of social economy and urbanization in China, the production and quantity of municipal wastewater are increasing. According to the forecast [1], China's urban sewage volume in the next 20 years will have a greater growth in 2010, the sewage discharge will reach 4.4 x 1010m3 / d-1. At present, China's annual output of dry sludge nearly 3 * 106t[2], along with the development of domestic sewage treatment, sewage treatment plant in the total water and the treatment level continues to expand and improve, the amount of sludge generated will also increase. A large number of sludge can not be timely and reasonable treatment to become a heavy burden on the sewage treatment plant.
Sludge also contains a large number of N, P, K, Ca and organic matter, and P, N in the organic state, can slow release, has a long-term effect. The sludge is useful to the rational use of biological resources, not only can increase the economic benefits of waste, therefore, to explore the effective treatment for the situation of our country and the use of sludge [3] technology has important practical significance.
1, the composition, characteristics and classification of sludge
Sludge is the product of sewage treatment, composition is very complex, it includes mixed sewage or industrial wastewater in the mud and sand, fiber, animal and plant residues and other solid particles and condensation floc by microorganisms, the formation of zooglea and adsorption of organic compounds, heavy metals and salts, a small amount of pathogenic microorganism and parasite egg comprehensive solid material [4]. The main characteristics of sludge is high moisture content (up to 99%), high organic content, easy to corrupt smelly, and fine particles, a smaller proportion of colloidal liquid.
There are many methods for the classification of sludge. According to the characteristics of the sludge, which can be divided into organic sludge and sediment; according to the treatment method of the waste water can be divided into: the primary sludge activated sludge, humus sludge chemical sludge; sludge produced according to different stage can be divided into: the raw sludge digestion sludge, sludge concentration and dehydration sludge drying. Sludge.
2, sludge treatment of new technologies
At present, the sludge treatment methods of domestic and foreign sewage treatment plants mainly include conditioning, concentration, dehydration, drying, digestion, composting and so on. [5]. These methods have exposed some shortcomings and deficiencies in engineering practice, so there are some new methods of sludge treatment to be applied in practice.
2.1 sludge wet oxidation process
Wet air oxidation (WO) is placed in a closed sludge reactor, under high temperature and high pressure air or oxygen as oxidant, according to the principle of submerged combustion oxidation of organic matter in sludge decomposition process of organic matter into inorganic compounds. The method is mainly applied to the treatment of all kinds of refractory organic sludge [6], the disadvantage is that the equipment is complex, operation and maintenance costs are high.
2.2 earthworm treatment sludge
Poland's BnrskO and Zambrow using earthworm effectively in wastewater treatment and sludge residue on sieve, a no smell, like humus and contains high nutrient fertilizer of earthworm. The digestive sludge of Changsha sewage treatment plant was treated by using earthworm, and the effect was good. Earthworms after purification treatment, sludge in Cu, Zn, Ni content decreased significantly after treatment; sludge into organic fertilizer particle smelly, loose, efficient, but after the earthworm treatment sludge with heavy metal enrichment, so as not to feed into the human food chain [7].
2.3 membrane bioreactor
Membrane bioreactor is a new technology which combines the membrane system in the membrane separation technology and the biological reactor in wastewater treatment engineering. Sludge retention time in membrane bioreactor is very long, and even can avoid sludge. However, the application of the method is limited by the blocking of membrane and the price of membrane material.
2.4 sludge acidification
Sludge acidification is a treatment method which is developed based on the characteristics of the high content of organic matter in excess sludge [3]. The basic principle is to return to the waste water treatment system with the residual sludge hydrolysis acidification, so as to achieve the purpose of reducing or basically no sludge discharge [8], the method is in the exploratory stage.
2.5 sludge constructed wetland treatment technology
Sludge artificial wetland treatment technology is a new type of sludge treatment technology, it is a set of sludge thickening, dewatering and degradation in one, can reduce capital and operating costs. According to reports, the Danish use of artificial wetland reed bed system for sludge dewatering and mineralization treatment, sludge due to dehydration and mineralization in the bed of the annual average of 90% and 96%. StevenT. has used the vertical flow wetland and horizontal flow wetland stability research on aquaculture sludge, the results show that two kinds of wetlands have better stabilization of [9] on sludge.
The main function of the treatment technology for sludge treatment is artificial substrate, microorganism and plant [10,11]. The artificial matrix provides stable surface attachment for microbial growth, provide nutrients for the carrier and resistant to water and sewage plant, and through some physical and chemical degradation of sewage plant sludge; in addition to the direct absorption and utilization of nutrients and adsorption, sludge enrichment of some toxic and harmful substances in water and oxygen resistance outside, and to the root zone maintenance of hydraulic transmission; microbial metabolism is the main mechanism of [12,13] degradation of organic pollutants in sewage sludge. At the same time, their mutual connection, reciprocal causation, form a system.
