Oxidation ditch is a variant of activated sludge method, whose aeration tank is in the form of a closed ditch, and whose aeration
The tank is in the form of a closed ditch, in which the mixture of sewage and activated sludge is circulated, and for this reason
is named. It is also known as "circulating aeration tank" and "aeration system without terminals" [2].
Oxidation ditch has a unique process characteristics, - generally do not have a primary settling tank, usually using delayed aeration.
Sludge load and sludge age selection should consider the sewage nitrification and sludge stabilization of two factors, generally
sludge age of l0d a 30d, sludge load in 0.05- 0.10kgBOD5/(kgMLSS.d) between. Oxygen
Chemical ditch on the removal of organic matter is very high, and its different combinations of processes also have the function of phosphorus denitrification.
In recent years, with the development of special equipment for oxidation ditch, technical equipment and operational control of
a whole set of technologies, such as the Netherlands DHV company and the United States EMICO company launched the cooperation of the Car-
rousel2000 oxidation ditch, the Danish Kruger company launched the alternating oxidation ditch, the United States En-
virex Company, the United States of America, the United States of America, the United States of America, the United States of America, the United States of America, the United States of America, the United States of America.
virex company introduced the Orbal oxidation ditch, Germany Passavant company introduced the brush aeration oxidation
ditch and so on.
Beijing Yanshan Petrochemical Company Niukouyu Wastewater Treatment Plant had oxidation ditch engineering test
test, the plant mainly accepts industrial wastewater and a small amount of domestic sewage, the results show that the Orbal oxidation ditch treatment
treatment is very good, the effluent of the indexes are much lower than the design value, COD, ammonia nitrogen removal rate of more than 90%
[3]; Deng Rongsen, Chongqing Architecture University, et al. Deng Rongsen et al.[4] from Chongqing Architecture University applied side channel oxidation ditch combined with anaerobic treatment method to treat high concentration organic wastewater (slaughtering), and the study showed that the combined oxidation ditch
treatment of high concentration organic wastewater is completely feasible, and the anaerobic combination can help to improve the quality of effluent, and the side
channel combination can realize the pump-less sludge automatic reflux; at present, the oxidation ditch is simple, easy to manage, and has the advantage of being a good treatment method. At present, oxidation ditch is widely used in small and medium-sized urban wastewater treatment plants in China for its simple process, convenient management and good treatment effect.
This process has a series of advantages such as simple process
, compact layout, flexible operation, good effect of phosphorus and nitrogen removal, etc. The disadvantage of this process is that it requires high self-control and complicated management.
In recent years, the rapid development of self-control technology for the SBR method again in-depth research and extensive
application, provides a very favorable prerequisites. Nowadays, the SBR method has developed into a simple, reliable, cost-effective and competitive municipal wastewater treatment technology, and many variations of the process have emerged based on it, such as the CAST (Cyclic Activated Sludge
Technology) process with intermittent aeration for intermittent water intake, CASS (Cyclic Activated Sludge System), ICEAS (Inten'nittent Cyclic Extended Aeration System) with continuous water intake and intermittent aeration.
He Zhanlong and Tang Yongming [5] used the SBR process to treat macaque farm wastewater, and the result was that the effluent quality
indicators were better than the GB8978- 1996 Comprehensive Wastewater Emission Standards, and reached the standards of animal
animal farm wastewater discharge standards; Yuan Zhong et al. [6] treated methanol wastewater with SBR, and the result showed that the treatment efficiency of the SBR process was better than the GB8978- 1996 Comprehensive Wastewater Discharge Standards, and the effluent quality of the SBR process was better than the GB8978- 1996 Comprehensive Wastewater Discharge Standards.
Ming et al.[7] used SBR to remove heavy metals in municipal sludge, and the results showed that the removal rate of Cu and Zn
reached 78.3% and 77.7%, and that of Cd was close to 99%, and the residual heavy metal content of leached sludge was consistent with the sludge content, and the residual heavy metal content of leached sludge was in accordance with the sludge content. The residual heavy metal content in the leachate treated sludge
meets the national standard of sludge agricultural use.
2.3 Anaerobic biological treatment
Anaerobic biological treatment is a treatment technology that utilizes parthenogenetic anaerobic bacteria and specialized anaerobic bacteria to degrade
organic pollutants under anaerobic conditions. Because of its high efficiency and low cost, it has become one of the modern advanced wastewater treatment
technology.
The anaerobic method is suitable for treating organic wastewater with high concentration. At the same time, anaerobic biological treatment technology
can produce 0.35m3 of methane per 1 kg of COD removed[8]. Therefore. Therefore, anaerobic treatment of wastewater is widely used in the
food brewing and sugar industries. Qiang Zhimin et al[9] utilized aerobic sludge to anaerobic
domestication method in an anaerobic composite bed (combining the advantages of an anoxic biofilter and UASB) inoculated with
culture, to treat wastewater containing phenol about l g/L, the treatment effect was obvious, the removal rate of phenol up to 98.7%,
COD removal rate of up to 98.3%.
The biggest disadvantage of anaerobic treatment of municipal wastewater is that the effluent quality usually fails to meet the discharge standards
, because anaerobic treatment mainly removes COD from the wastewater, resulting in higher concentrations of ammonia, nitrogen, and sulfide in the effluent water, and some of the sensory indicators, such as chromaticity and odor, are also heavy. For the treated effluent in the
BOD, TSS, N, P and pathogens / pathogenic microorganisms such as biological methods (such as stabilization
ponds), physicochemical methods (such as lime dosing method, etc.) and chemical methods (such as the addition of O3, etc. to remove).
In the anaerobic treatment of wastewater, it is worth noting that the treatment temperature and concentration of wastewater, temperature
affects the degradation of dissolved organic matter, the hydrolysis of organic matter at temperatures lower than 20 degrees Celsius will be
inhibited[10], and the concentration of the wastewater affects the rate of growth of anaerobic microorganisms.
2.4 Natural purification system
Natural biological treatment is a technology that utilizes microorganisms that grow and reproduce under natural conditions to treat wastewater
. Its main characteristics are simple process, construction and operation costs are low, but the purification function
constrained by natural conditions. The main treatment technologies include land treatment, artificial wetlands and stabilization ponds
. The following mainly introduces the application of land treatment and artificial wetland in sewage treatment.
2.4.1 Land treatment method
Land treatment method is to use the ecosystem composed of soil, microorganisms and plants to physically, chemically and biologically purify the pollutants in the sewage, and through the systematic nutrient and water cycle
loop utilization, so that the green plants can grow and reproduce, thus realizing the resourcefulness, harmlessness and stabilization of sewage
. p>
Chemical, is a kind of high efficiency, energy saving, economic and ecological principles of sewage treatment system.
There are five basic types of sewage land treatment technology: slow percolation, rapid percolation, underground percolation
filtration, surface diffusion and wetland systems. The range of wastewater treatment for each type is shown in Table 1 [11].
The selection of process type for land treatment system is mainly based on the nature of soil, permeability, topography, type of plant
crops, climatic conditions and requirements for the degree of wastewater treatment.
2.4.2 Artificial wetland treatment system
Artificial wetland is developed in the 1970s and 1980s. It is a wastewater treatment
method that utilizes the physical, chemical and biological synergies in the wetland
natural ecosystem to achieve efficient purification of wastewater through filtration, adsorption, ****-sedimentation,
ion exchange, plant adsorption and microbial decomposition[12].
Artificial wetland removes a wide range of pollutants ,including N ,P ,SS, organic matter, trace elements
elements, pathogens and so on. Peng Chaoying et al[13] explored and tested the artificial wetland in a certain place, and the results showed that the CODCr removal rate could reach 83% and the total nitrogen removal rate could reach 45%.Li Yazhi[14] and others used a water
cucurbit and a watercress artificial wetland system for the treatment of recycled pulp and paper wastewater. The results showed that:
The removal rates of BOD5, CODCr and SS reached 98%, 93% and 89%, respectively, and the system performance was stable. The effluent water quality meets the discharge standard and can be used for agricultural irrigation.
3. Summary
(1) Oxygenated ditch process and SBR process are the preferred processes for urban wastewater treatment, first of all, its
cost of infrastructure is significantly lower than the conventional activated sludge method, A/O, A2/O method, and the treatment effect is relatively
good; (2) Anaerobic biological treatment is a low-cost, low-energy, low-sludge production, and the system performance is stable
and the effluent quality meets the discharge standard and can be used for agricultural irrigation.
And the combination of wastewater treatment and energy recycling, is the preferred technology for most developing
countries, including China; (3) natural purification system as an ancient sewage purification system, due to
has the superiority of other wastewater treatment technologies can not be compared to the world has always been widely
popular attention, especially in the small and medium-sized towns of sewage treatment plant has the potential to be the best choice for the development of the sewage treatment system, the most important thing is that the system can be used for the treatment of wastewater. Small and medium-sized town sewage treatment plants have a broad application prospects.