Shorcut biological nitrogen removal is a non conventional way of removing nitrogen from wastewater using two processes either nitrite shunt or deammonification. In the nitrite shunt process, the ammonia oxidation step stops at the nitrite stage, which is known as partial nitrification, then nitrite is directly reduced to nitrogen gas. Effective partial nitrification could be achieved by accumulating Ammonia Oxidizing Bacteria (AOB) and inhibiting Nitrite Oxidazing Bacteria (NOB).
The excessive nitrogenous compounds withdrawn in water streams from the effluent of wastewater treatment plants causes numerous problems for the aquatic system as it leads to eutrophication causing the excessive growth of algae and increase in the oxygen depletion and poisons in the aquatic life. To avoid the aforementioned negatifve effects, reducing this compounds level has been a manner of great importance either by physical-chemical processes or biological processes. Due to its higher efficiency and lower cost over physical-chemical processes, Biological Nitrogen Removal (BNR) processes have been adopted widely. Conventional BNR processes comprise two main practices: nitrification and denitrification. Nitrification is the aerobic biological conversion of ammonia to nitrate with oxygen as electron acceptor via a group of autotrophic bacteria through two steps involving Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB), respectively. However, these two steps conventional BNR processes require 2mol of oxygen to oxidize the ammonia to nitrate. Afterthough, the nitrate is reduced via heterotrophic bacteria to nitrite and nitrogen gas, which also requires organic matter during the denitrification stage.
Hence, conventional BNR processes require high oxygen and external carbon sources along with a slow growth of the autotrophic and heterotrophic bacteria. To overcome the aforementioned challenges and reduce the energy required for nitrogen removal of side stream high ammonia waste streams, Shortcut Biological Nitrogen Removal (SBNR) has ebeen developed. Based on the fact that nitrite is an intermediat compound in both nitrification and denitrification, SBNR relies on the direct conversion of nitrite produced in the first step of nitrification to atmospheric nitrogen instead of oxidizing it to nitrate then reducing the latter back to the former.Shortcut Biological Nitrogen Removal implies the reduction of oxygen consumption during the aerobic phase by 25% as aresult of skipping the nitrite oxidation to nitrate and consequently reduces the total energy required by 60%. Additionally, SBNR eliminates the use of external electrone donor by 40%; resulting from skipping the nitrate reduction to nitrite; which makes it suitable for wastewaterwith low carbon to nitrogen ratio. Shotcut Biological Nitrogen Removal also results in a significant decrease of the sludge production in nitrification and denitrification processes by 35% and 55%, respectively. The SBNR process comprises both nitrite shunt and deammonification processes. In the deammonification process, 50% of the ammonia is oxidized to nitrite subsequently the remaining ammonia is oxidized anaerobically to nitrogen gas using the nitrite produced as electron acceptor carried out by Anaerobic Ammonium Oxidizing (Annamox) bacteria.
With the rapid development of economy of the Three Gorges Resevoir area, a large amount of high salinity and high nitrogen organic wastewater about 3,5 million m3 per year is discharged by The Fuling Mustard Tuber Industry. It poses a serious threat to the water environtment of reservoir.
High salinity is a key problem that affects the processes of biological treatment for Fuling Mustard Tuber waste water. In recent years, the effects of salinity on the activities of microorganism in bioreactors were studied. The studies have showed that high salinity in wastewater typically dampens the degrading enzymes and decreases cell activity, can even cauuse cell plasmolysis, and its also have negative effects on organic removal. Generally, high salinity wastewater needs to be diluted before treating , it means the long process flow and low operation load which demand gigantic investment and high operating cost. Consequently, building a microbial communityof salt-tolerant halophilic microorganisms that can improve the adaptability of system to high salinity is the key to treat the high salinity wastewater.
How to remove the nitrogen high salinity and high nitrogenorganic wastewater is another key problem. Traditionally, the nitrogen removal process were based on the autotrophic nitrification and heterotrophic denitrification. But high salinity wastewater can effect the conventional processes of ammonium oxidation, nitrification and denitrification. the traditional process of autotrophic nitrification was inhibited by organic matter.Therefore, the simultaneous removal efficiency of nitrogen and COD was low, Meanwhile, the low organic loading of outotrophic nitrification reactor can lead to large reactor volume, high investment and high operating cost. With the proposed concept of the heterotrophic nitrification and aerobic denitrification, heterotropic nitrification bacteria gradually was known by the public. Comparing with traditional nitrogen removal methods, neterotrophic nitrification has swveral advantages. Heterophic nitrification bacteria can remove COD and nitrogen simultaneouslyin one reactor via simultaneous nitrification and denitrification. Heterotrophic nitrification bacteria have the ability to utilize different kinds of materials. And it is conducive to coexist with other strains. Meanwhile, some species of heterotrophic nitrification bacteria have the charactheristic of high level ammonia resistant.These features of heterotrophic nitrification bacteria have great significance for treating the high salinity and high nitrogen organic wastewater. Recent studies of heterotrophic nitrification bacteria mainly focused on substrate removal, accumulation of intermediates, and the removal of COD and nitrogen via simultaneous nitrification and denitrification. But the applications of the heterotrophic nitrification -aerobic denitrificationhave been isolated, but they could not perform well in nitrogen removal with high salinity.
A simultaneous nitrogen removal system for high salinity and high nitrogen organic wastewater via heterotrophic nitrification was developed in a pressurized biofilm reactor. During the experiment, there is no anaerobic-aerobic conditionsand no excess sludge discharge in the single stage reactor. The perfomance of COD and nitrogen removal were examined. Meanwhile, PCR-DGGE was used to detectthe microbial diversity and community structure. This study can provide a more efficient and feasible solution to treat the high salinity and high nitrogen organic wastewater.
Nowdays, many wastewaters do not contain sufficient amounts of biodegradable carbon, making them less suitable for nitrogen removal via nitrification-denitrification process. Moreover, with the development of anaerobic treatment process, most organic compounds in waste water are converted to biogas, which is feasible with the present state of the art. The autotrophic nitrogen removal process which based on partial nitrification and anaerobic ammonia oxidation (Anammox) could remove nitrogen from wastewater with no organic consumption, which has attracted increasing attention because of its ability to achine high nitrogen removal rate with less energy consumption. So it could be alternative technology for treating the sewage with low ratio of COD to nitrogen(C/N). The autotrophic nitrogen removal technology include two process type partial nitrification-anaerobic ammonia oxidation and completely autotrophic nitrogen removal over nitrite. since the occurence of anaerobic ammonia oxidation requires a certainproportion of nitrite nitrogen of 1.32 in the feed solution, part of ammmonia in the wastewater should be oxidized to nitrite for the uptake by anaerob ammonia oxidazing bacteria. Thus, the partial nitrificationprocess which undertakes the oxidation of ammonia to nitrite is critical and indispensable for the autotrophicnitrogen removal from low C/N sewage.
In partial nitrification process, the oxidation of ammonia to nitrite by ammonia oxidizing bacteria should be enhanced while the oxidation of nitrite to nitrate by nitrite oxidizing bacteria should be inhibited since anaerob ammonia oxidizing bacteria consumes only ammonia and nitrite. in consequence, a prominent and stable partial nitrification requires enrichment of ammonia oxidizing bacteria and inhibition of nitrite oxidizing bacteria, to achieve high ammonia removal efficiency and nitrite accumulation rate. It didn’t seemquite so difficult to achieve high rate and stable partial nitrification when treating sewage with high temperature or high ammonia in side-stream such as sludge digestion and landfill leachate with. However, there were still some challenges in partial nitrogen process for treating the main stream sewage with low ammonia or low temperature such as the influent of municipal plant. On one hand, the oxidation rate of ammoniaby ammonia oxidizing bacteriais severely affected by temperature, the lower temperature would lead to lower ammonia removal efficency. Moreover, the higher activation energy of ammonia oxidizing bacteria than nitrite oxidizing bacteria resulted in the difficulty of nitrite accumulation under low temperature, and many studies have reported failure during winter temperature. On the other hand,the lower ammonia concentration would also impose restriction on partial nitrogen process, since the lower free ammoniacould not perform effectivesuppression on nitrogen oxidizing bacteria, In conclucion, the low temperature and ammonia concentrationwould not limit the efficiency, but also effect the stability of partial nitrogen, so the low ammonia sewage treated system could not reach the effuent demand in winter temperature. The operation of minicipal plant in winter was one problems that could not be ignored during the application of partial nitrogen, thus it was essential to gain more information about the performance and microbial characteristics of this process under low temperature.
Generally, there are two kinds of waste water treatment systems, including activating sludge system and biofilm system, in which organisms respectively survived in suspended and fixed condition. Activated sludge systemcoul achieve high removal loading since its better mass transfer, which could be flexiblyoperated and controlled. For biofilm system, it enables a larger biodiversity of the microorganism due to its long SRT, and has shown great potentials for partial nitrogen as aresult of sufficient oxygen usage and well stratified distribution of ammonia oxidizing bacteria and nitrogen oxidizing bacteria within the biofilm. In previous studies, pertial nitrogen reactors have been conventionally operated as activated sludge system, whereas it has been confirmed that biofilmpartial nitrogen processes with attached biomass also have advantages. Both the two systems could be effectively used for partial nitrogen process, but it was doubtless that the suitable operational condition could be different between each other. However, no study has been done simultaneously in both in two systems and the specific suitable strategies for each system were still not clear, let alone for treating sewage in main stream.
Nitrogen compunds wastewaters must be removed because they cause environmental problems including dissolved oxygen depletion, eutrophication, odor, ammonia toxicity, and ground water contamination. Biological nitrogen removal involving nitrification and denitrification has been still adopted in wastewater treatment because it is inexpensive and causes little envoromental damage, in contrast to physico-chemical treatments. Nitrification, the first step in biological nitrogen removal, involves two processes. Ammonia oxidation to nitrite by ammonia oxidazing bacteria and nitrite oxidation to nitrate bay nitrite oxidizing bacteria. Ammonia oxidation though to be the rate-limiting step in nitrification, bacause ammonia oxidizing bacteria have lower growth rate than nitrite oxidizing bacteria, and are more sensitive to inhibition by environtmental factors. Therefore, to establish the stable nitrification reaction in waste-water treatment process the dynamics of ammonia oxidizing bacteria in response to the operating condition must be understood.
The substrate consistency is one of the important factors to ensure process stability of biological system. However, substrate concentration often fluctuate in full-scale wastewater treatment plants. Substrate overload reduces microbial activity, which results in the poor removal efficiency. Similarly, ammonia overload resulting from variations in substrate content can cause failure of ammonia oxidation in nitrification system. Ammonia oxidizing bacteria are much more sensitive to substrate concentration rather than are heterotrophic bbacteria grown in wastewater treatment plans. For example, ammonia oxidizing bacteria can be inhibited only 1.0mM of free ammonia concentration, although some heterotrophic bacteria can effieciently grow at 1.0% of glucose (55,5mM).
The steel manufacturing industry produces large amounts of steel wastewater that contains high concentration of ammonia (>100ppm) and inorganic salts as a by product of a process. Steel wastewater has 6,4<pH<8,9 This high concentration of ammonia can often cause ammonia overloading shock to biological nitrogen removal system, thus its reducing nitrification efficiency. In some steel wastewater systemtreatment plans, the high strength of ammonia wastewater used introduced into nitrification system can change suddenly, thereby causing a drastic increase of ammonia concentration. Therefore, for nitrification of steel wastewaterto be succesful, the effect of ammonia overloading shock on the nitrification resilience of the ammonia oxidizing bacteria must be determined.
Certain ammonia oxidizing bacteria species appear to adapt to biological nitrogen removal systems that are subject to ammonia overloading shock, and become the dominant species in the ammonia oxidizing bacteria community. Hence, microbial community resilience following ammonia overloading can contributing in accelerating nitrification step in full-sacle steel wastewater treatment facilities. However only a few studies have been conducted regarding the process resilience under ammonia overloading shock. For example, actvated sludgepre-exposed to high ammonia level had higher resistance to ammonia than did un-acclimatedactivated sludge, and the dominant ammonia oxidazing bacteriacommunity was changed after the ammonia overload period in a sequential batch reactor system. However, the information of the effects of ammonia overloading shock on process resilience and ammonia oxidizing bacteria communities have been still limited.
Constructed wetlands, simulating purification of natural wetlands, have become widely applied technique and valuable complemet to traditional wastewater treatment systems in recent years. Low cost, convenient operation and maintenance and high wastewater treatment efficiency are the major advantages of constructed wetland . Although the quantities of constructed wetklands have increase year by year, the nitrogent (N) treatment performance has always been unsatisfactory, which is a major challenge for constructed wetlands.
Oxygen supply has been commonly perceived as a limiting factor to N removal efficiency. The use of constructed wetlands could overcome this problem because of its unique structure, consisting of a down-flow chamber and up-flow chamber. Therefore, the U-shaped flow structure of integrated vertical-flow constructed wetlands gave rise to the alternating “aerobic-anoxic-anaerobic=anoxic-aerobic” multifunction layer, i.e., a gradient of physical, chemical and biological condition favorable for microbial growth and reproduction. This is especially important for enhancing the function of N removal bacteria whose oxigent requirement is different.
The competition of N removal microbes in the environtments is the key issue for the nitrogen removal pathway. Moreover, the influent C/N ratio also played a crucial role in denitrification which is ussually restricted by thje lack of organic carbon source. Very few studies have been focused on the relationship between N removal microbes and influent C/N ratio (2:1, 4:1,6:1 and 8:1) nad to reveal the link berween the functional genes of microbes and N conversion reactions. The qPCR technologywas employed to quantify the abundance of key functional genes involved in N removal.
The problem of over fishing in public waters has led to aquaculture increasingly gaining importancw for global fis supply. Currently aquaculture continue to be the fastest growing animal food producing sector, already generating 50% of global fishsupply FAO-Food and Agriculture Organization of the United Nations. Conventional fish farming methods are rarely sustainable. They produce large amount of nutrient rich waste water, partially loaded with chemical use for fish treatment, which has harmful effect on the receiving aquatic environtment.. In 2009, Europen Commission proposed a strategy for the future of europen aquaculture for sustanable development of this sector. Aquaponic, which is combines the aquaculture of fish with the hydroponic cultivation of plants in a closed water cycle, can contribute to solving the problems outlined by European Commission on the way toward sustainable aquaculture by:
- Saving water; Aquaponics uses small amounts of fresh waters
- Guaranteeing product safety; Aquaponic uses no antibiotics and/or pesticides
- Protecting the environtment; Aquaponics effecientlyreduces nutrient emissions and is thus a hogh level strategy in the fight against eutrophication
A monitored pilot operation of aquaponics under field conditions, a small scale land based cyprinid fish farm with a diversion of arecirculating water into closed loop system with a treatment chain consisting lamellar settler, a rougfing filter, a vertical constructed wetland planted with tomatoes (lycopersion esculentum Mill) and ultrasoun device. The most significant advantages of constructed wetland are the utilisation of natural processes and their cost effectiveness . By planting crop plants in vertical constructed wetland, the aquaculture effuent is recirculated over tricling filters or ather suitable substarates in which crop plants are grown. This special type of vertical constructed wetland provide the necessary nitrification rates for a recirculating aquaculture.
A possible solution for a chemical free aquaculture could be the use of ultra sound devices to reduce pathogenic bacteria in fish ponds and to counteract algae growth. Thus, high pH values during day, oxygen drops at night, and large quantities of organic matter in fish ponds can be avoided.
In contrast to the investigated aquaponic system, other recirculating aquaculture systems (RAS) ussualy apply a biological wastewater treatment mainly as biofil reactor, biofilters, moving beds, and activated sludge processes. However, due to relatively high cost and unstable operation, RAS are not yet widespread. The presented multi-fuctional integrated technology has all the benefits of physical water treatment without the use of any chemicals, since ultrasound device acts as algae inhibitor, while water circulation can contribute to nutrient retension and usage by plants as well as to water savings in accordance with European water policy.