1、The ways of regular sludge and oily sludge treating Generally speaking， there is a procedure for treating sludge after secondary treatment of wastewater if we want to prevent our living environment from second polluting. Wastewater treatment objectives are accomplished by concentrating impurities in
2、to solid form and then separating these solids from the bulk liquid. This concentration of solids， referred to as sludge， contains many objectionable materials and must be disposed of properly. Sludge disposal facilities usually represent 40 to 60 percent of disposed of the construction cost wastewa
3、ter-treatment plants， account for as much as 50 percent of the operating cost， and are the cause of a disproportionate share of operating difficulties. First of all， the initial sludge is separated from the clean water lying upon it in the secondary clarifier by pumping it to a tank. Because the ini
4、tial sludge have a high water content that usually can up to 99.5 percent in volume， sludge thickening is a necessary procedure， and there are several techniques are available foe volume reduction. Mechanical methods such as vacuum filtration and centrifugation may be used where the sludge is subseq
5、uently to be handled in a semisolid state. There methods are commonly used preceding sludge incineration. Where further biological treatment is intend， volume reduction by gravity thickening or flotation is common practice. In both cases， the sludge remains in a liquid state. Gravity thickeners are
6、very similar in design and operation to the secondary clarifiers used in wastewater treating systems. The thickening function is the major design parameter， and tanks are generally deeper than secondary clarifiers to provide greater thickening capacity. A well-designed， well-operated gravity thicken
7、er should be able to， at least double the solids content of the sludge. In another word， the water content ratio of sludge can be reduced from 99.5 percent in volume to 98 percent or ever much more reduction. It should be noted that the design of gravity thickeners should be based on the results of
8、pilot plant analysis wherever possible， since successful loading rates are highly dependent on the nature of the sludge. In dissolved air flotation， a small quantity of water， usually secondary effluent is subjected to aeration under a pressure of about 400kPa. This supersaturated liquid is then rel
9、ease near the bottom of a tank through which the sludge is passed at atmospheric pressure. The air is release in the form of very small bubbles that attach them selves to， or become entrapped in， the sludge solids， floating the solids to the surface. The thickened sludge is skimmed off at the top of
10、 the tank while the liquid is removed near the bottom and is returned to the aerator. After volume reducing， sludge represents a considerable hazard to the environment and must be rendered inert prior to disposal. The most common means of stabilizing is by biological degradation. Because this proces
11、s is intended to convert solids to unicellular end products， the term digestion is commonly applied to this process. Sludge digestion serves both to reduce the volume of the thickened sludge still further and to render the remaining solids inert and relatively pathogen-free. These goals can be accom
12、plished by either anaerobic or aerobic digestion. Sludge contains a wide variety of organisms， and thus requires a wide variety of organisms for its decomposition. The literature relating to anaerobic sludge digestion often divides the organisms into two kinds， the acid formers and the methane forme
13、rs. So we can divide the anaerobic sludge digestion into two steps too. On the first step， the acid formers consist of facultative and anaerobic bacteria that solubilize the organic solids through hydrolysis. The soluble products are then fermented to acids and alcohols of low molecular weight. The
14、second step， the methane formers consist of strict anaerobic bacteria that convert the acids and alcohols， along with hydrogen and carbon dioxides to methane. Because this two kings bacteria can keep themselves living in oxygen-less surroundings， reactor for anaerobic digesters must be closed. Other
15、 parameter such as reacting temperature， pH value and turbulence of the mixture should be considered to design the tank. Sludge can also be stabilized by aerobic digestion. Generally restricted to biological sludge in the absence of primary sludge， this process is essentially a continuation of the a
16、eration process， with the volume being reduced by thickening in the secondary clarifier and sludge thickener. The most common application of aeration digestion involves stabilizing sludge wasted from extended aerobic systems. Then， aerobic digestion is not as sensitive to environmental factors as is
17、 its anaerobic counterpart and is not as subject to upsets. After sludge digestion， the organics can be removed and the volume of sludge can be reduced by further. Then， the sludge needs disposed. Several potions are available for the ultimate disposal of sludge. These include incineration， placemen
18、t in a sanitary landfill， and incorporation into as a fertilizer or soil conditioner. Raw sludge can be incinerated， provided the water content is sufficiently reduced. Supplement fuel is necessary to initiate and maintain combustion and municipal solid waste may be used for this purpose. Raw or dig
19、estion sludge can be also be disposed of in sanitary landfills. Land application of sludge has been practiced for many years， modern application being limited to digested sludge. The nutrient value of the sludge is beneficial to vegetation， and its granular nature may serve as a soil conditioner. It
20、s application has been limited to ground used for forage crops for nonhuman consumption， although the possibility of its use on ground used to grow edible produce is still being investigated. Metal toxicity in plants and water pollution from excess nitrates appear to be the limiting factors in land
21、application of sludge. Sludge may be applied in a liquid state by spraying， ridge and furrow， or by direct injection beneath the soil. Dewatered sludge may be spread on the land and cultivated into the soil by conventional agricultural equipment. We see the treatment of sludge as a regular treating
22、what have been mentioned in the front of this writings. The sludge will contribute to the environment polluting， so we should be do our best to make the sludge hazardless. Now， some sludge of more different characteristics which leading different kinds of environment polluting are investigated. In t
23、his writings， I will talk something about oily sludge which can be saw as a topic sludge produced from our oil production and processing activities. A huge amount of oily sludge is produced， and this sludge usually contains a considerable quantity of oil， which should be removed before its finally d
24、isposal. Generated in a vast amount in petroleum refinery plants oily sludge cannot be safely disposed unless its oil content is reduced below a certain limit. In addition， the vast amounts if oil sludge generated in refineries from water-oil separation systems and accumulation of waste oily materia
25、ls in crude oil storage tanks poses great problem because of the expensive disposal and its large harmfulness of environment. Petroleum is a complex mixture of non-aqueous and hydrophobic components like n-alkane， aromatics， resins and asphalt. Many of these components are toxic， mutagenic and carci
26、nogenic. Therefore， their release to the environment is strictly controlled and they are classified as priority environmental pollutants by the US Environmental Protection Agency due to their adverse impact on human health and environment. A variety of methods have been suggested to treat oily sludg
27、e. There are physical or chemical methods such as incineration， chlorination， ozonation， and combustion， biological treatment such as bioremediation， conventional composting and so on. Nowadays， with the technology of oily sludge treatment developing， separation of oil from oily sludge by freezing a
28、nd thawing and the oily sludge bioremediation could be more attractive ways Freeze/thaw treatment is generally accepted as a physical sludge conditioning method that can significantly improve certain sludge dewatering characteristics， change the floc structure into a more compact form and reduce the
29、 sludge bound water content .Once the so-called gross-migration“ of flocs occurs， freezing front would reject impurities in the solution to the far-ends of the vessel， thereby achieving concentration purposes recently discussed the benefit obtainable from freeze/thaw treatment. To our best knowledge
30、， there is no work appearing in literature having discussed the feasibility of employment of freeze/thaw treatment for separating oil from the oily sludge. But as natural freezing is easily accessible in many countries， if feasible， freeze/thaw treatment may provide an alternative for oily sludge tr
31、eatment and disposal. Comparing the result from freeze/thaw treatment to regular treatment， we can find that after thawing， however， an oil layer gradually appeared at the top of the sample. Finally， three layers stood clearly in the tube: at the top was a clear， transparent oil layer； at the bottom
32、， a deep-dark sediment layer， while in between， a water layer. Still settling of original sludge for 24 h leads to a clear supernatant and a deep-dark sediment. No oil phase could be visually observed. The above-mentioned results clearly reveal that， simple freezing and thawing treatment can efficie
33、ntly separate oil. The physico-chemical treatments can be applied for the oily sludge， but these methods are extremely expensive. Composting and bioremediation with an introduction of oil degrading microorganisms (bio-augmentation) or activation of indigenous ones are now considered as two major eco
34、nomic methods for the decontamination of oil pollutions. Composting has some visible advantages including relatively low capital and maintenance costs， simple design and operation and some (but incomplete) removal of oil pollution. However， in general， the efficiency of composting is unsatisfact- or
35、y to meet the current environmental regulations. For more content of the oil， the oily sludge is much more difficult for the bioremediation. Numerous researches have demonstrated high bioremediation efficiency for oil polluted soils， but these methods have limitations for the oily sludge mainly deal
36、t with extremely high pollution level. Most of the experiments were carried out in the lab ， while the field experiments were very few. The bioremediation treatment of the oily sludge was just beginning. These experiments were meaningful for the advance of this technology. There is a study of oily s
37、ludge treating in China during 2004. The bioremedia- tion by augmentation of biopreparation was compared with a conventional composting. The oily sludge and oil polluted soil were received from an oil production plant. The total hydrocarbon content (THC) varied from 327.7 to 371.2 g kg-1 of dry slud
38、ge and the THC in contaminated soil was 151.0 g kg-1. Before application of preparation， straw， sawdust， top sand and pure soil were added in different proportions to the sludge and soil and mixed thoroughly. Such sludge and soil composites were used for negative controls and for activation of indig
39、enous oil degrading microorganisms with addition of fertilizer (positive controls). For composting， crude manure and straw were added to the oily sludge and the THC was 101.4 g kg-1. The biopreparation was applied every 2 weeks and experiment lasted 56 days under the ambient temperature. The sludge
40、was mixed and watered every 3 days. After three times of biopreparation application， the THC decreased by 4653% in the oily sludge and soil， while in the positive controls (activation of indigenous microorganisms) the THC decreased by 1323%， and there was no oil degradation in negative controls After composting， the THC decreased by 31% in the oily sludge. The above-mentioned phenomenon clearly reveals that， bioremediation will be an effective way to deal with oily-sludge more efficiently as well as economically.
