«CARBONACEOUS, NITROGENOUS AND PHOSPHORUS MATTERS REMOVAL FROM DOMESTIC WASTEWATER BY AN ACTIVATED SLUDGE REACTOR OF NITRIFICATION-DENITRIFICATION ...»
Journal of Engineering Science and Technology
Vol. 4, No. 1 (2009) 69 - 80
© School of Engineering, Taylor’s University College
CARBONACEOUS, NITROGENOUS AND PHOSPHORUS
MATTERS REMOVAL FROM DOMESTIC WASTEWATER
BY AN ACTIVATED SLUDGE REACTOR OF
MOHAMAD ALI FULAZZAKY
Keyword: Anoxic-aerobic reactor, Activated sludge, Simultaneous pollutant elements removal.
69 70 M. A. Fulazzaky Nomenclatures Qt Inlet and outlet flows rs Organic pollutants diminution rate rx Microorganisms growth rate S Organic pollutants in effluent Sm
1. Introduction The major part of Asian countries from the year-to-year facing the environment degradation due to the population growth as well as the economic development whereas the development’s actors have yet consider correctly applying the 3 pillars of the UN framework of sustainable development, i.e., the economic, social and environmental aspects. Degradation of living environment mainly in the developing countries is remarkably urged to the high economic development and population growth in the last decades. Of course, it brings to the difficult condition therein the tendency of conflict interest between the economic development demands and sustainability of environmental balance. This paper is proposed to promote the appropriate engineering approach which may be considered to apply the activated sludge based on biotechnology method in management of wastewater to improve the quality of environment.
The original quasi-totality of pollutants coming from domestic wastewater composing three major elements – i.e., carbon, nitrogen and phosphor thereof, the biological process is used to remove these elements and the procedure of controlling the amount of activated sludge in the reactor is conventionally utilized to a unit of domestic wastewater treatment plant. It is clearly to remove carbonaceous and nitrogenous pollutants which are effectively proceed in the biological treatment plant and, this technology has been fixed to the definitive design of environmental engineering. But the biological procedure of phosphorous pollutants removal has yet consider as suitable technology in the formality engineering design. Thereby, the chemical precipitation procedure is technically recommended to reduce the phosphorous matter which contains in domestic wastewater in order to achieve the admissible norm at the expected value of effluent standard.
Managing the amount of activated sludge is promoted to carry out controlling of reactor’s loads – hereby expressed as art of biological wastewater treatment process – realizing the maintaining of the content of SS at certain quantity.
Defining the age of sludge and maintaining the reactor with suitable condition, it is possible to realize the implementation of this technology. Whereof, it exists three categories of treatment procedure, i.e., low, medium and high loads of reactor that have been technically adopted to remove the organic pollutants accompanying domestic wastewater. Using the mass balance expression it is possible to carry out monitoring of the SS in the influent and the effluent and to regulate the reactor’s loads which purge the amount of sludge periodically.
Journal of Engineering Science and Technology March 2009, Vol. 4(1) Carbonaceous, Nitrogenous and Phosphorus Matters Removal 71
2. Configuration of Pilot Plant The main objective of the configuration of pilot plant is clearly to have a design that can be applied by using activated sludge to reduce the major pollutant elements of domestic effluent. Thereafter, the treated wastewater may be directly ejected to the river or other destined natural ecosystem. Regarding the application of this technology in the developing countries it is considerable to design a simple hydraulic engineering infrastructure which is able to match with the local conditions.
This configuration is tendency selected the total oxidation process system or the category of low loads reactor that characterizes with the hydraulic time of 12 hours and the age of sludge of 15 days as well as the recycle discharge of activated sludge is over than 100% . The schematic chart of domestic wastewater pilot plant is shown in Fig. 1 and the principle dimensions are described in Table 1.
Pump Sludge Purged influent Iron Ferric Tank Pump Pump
Standard operational procedure is used to run the biological treatment process
that can be successively proposed to do through several steps as follows:
1. Raw domestic wastewater is collected in the equalization tank and maintained temperature at 4oC and also it is necessary to stir wastewater that being sure mixed completely;
Journal of Engineering Science and Technology March 2009, Vol. 4(1) 72 M. A. Fulazzaky
2. Pumping the influent with a regulated discharge into the reactor and controlling the amount of activated sludge by monitoring the concentration of SS in the influent and in the effluent;
3. Efficiency of reactor is initially verified by monitoring the concentrations of COD, NH4+ and PO43- at certain time; and
4. Efficiency of reactor related to remove carbon, nitrogen and phosphorus elements is verified by monitoring the concentrations of COD, NH4+, NO3- and PO43- in conformity with the biological process step of nitrification-denitrification and the biological-chemical process step of phosphorous precipitation.
Eliminating three major pollutant elements, i.e., carbon, nitrogen and phosphor by using an anoxic-aerobic reactor is essential to follow three successively steps. Firstly, elimination of the carbonaceous matter is accomplished by setting the reactor into an aerobic condition. Secondly, elimination of the carbonaceous and nitrogenous matters simultaneously is practiced by modifying the complex media of reactor from the aerobic condition to anoxic-aerobic condition which is capable to bring this culture media of activated sludge from aerobic to facultative reactor of nitrification-denitrification type. And finally, the elimination of the carbonaceous, nitrogenous and phosphorous matters simultaneously is carried out after the cycle of nitrificationdenitrification is stable. Whereby, in this step the reduction of these matters is regularly affected by adding the ferric iron (FeCl3.6H2O) into the reactor.
3. Characteristics of Domestic Wastewater The impurities present in domestic wastewater consisting the organic and inorganic matters entrained by the liquid flow in the form of suspended solids – settleable floating and colloidal – or, to a varying extent, matter dissolved in the water. To such matter it contains microorganisms liable to decompose organic matter and cause putrid fermentation . One of the main characteristics of domestic wastewater is biodegradable, and depending of a food balance supplied to bacteria. The characteristics of domestic wastewater applying in this study which are remarked the ratio of the soluble to total matters in the raw wastewater is about 50% such as the average value of soluble COD is 279 mgO2/L and this of total COD is 504 mgO2/L as well as the average value of soluble phosphorus is
5.5 mgP/L and this of total phosphorus is 10.5 mgP/L, as shows in Table 2.
Regarding the carbonaceous and nitrogenous matters as well as the solid particles are characterized by the moderate concentration of untreated domestic wastewater  while the phosphorous matters accompanying domestic wastewater theoretically present different compounds of phosphor with the total concentration range varies from 10 to 25 mgP/L which corresponds to the domestic pollutant loads of 3.9 to 4.2 grams of phosphor per equivalent inhabitant per day . One part of 50 to 70% is in the form of orthophosphate and the rest is in form of polyphosphate and organic phosphorus . During the transportation of domestic wastewater in the sewerage network system of a city, the polyphosphate and organic phosphorus containing the sewage transferred by hydrolysis process into the form of orthophosphate and, finally after passing the wastewater treatment plant the phosphorous compound in the clarify effluent remains about 90% in the form of orthophosphate .
The characteristics of domestic wastewater from Labege’s municipality present in Table 2 which is indicated by the concentration of total phosphorus of 5.5 to 12.5 mgP/L, it is possible to consider that the loss of phosphorous matter during the transportation in the sewerage network system is caused by transferring the biodegradation organic matter into the biomass and by settling the phosphor through chemical precipitation onto the partition of ditch along the sewerage system.
4. Methodology to Control the Reactor The capacity of reactor is designed to accommodate the discharge of influent which maintaining the hydraulic retention time of 12 hours and the reactor’s loads of 3 g/L of SS. Wherewith, the age of activated sludge is regulated to 15 days [1,7]. Sludge is also called as complex media which is necessary with stirring continuously to maintain in homogeneity.
Setting up the reactor into aerobic condition at the beginning should be affected by aeration in order to conserve the dissolved oxygen (DO) is about 2 mgO2/L and it is necessary to maintain this condition in order that the biological process is stable identifying the effectiveness of wastewater treatment more than 85% of carbonaceous pollutant with, the concentration of COD is below of 100 mgO2/L and the Molhman’s index is below 120 mL/L .
Nitrification phenomenon is naturally taking place in the reactor by using dissolved oxygen due to the presence of aerobic and autotrophic bacteria while starting the nitrosomonas bacteria catalyzes oxidation process in order to change nitrogenous matters from ammonium to nitrite form and pursuit the nitrobacter acts to complete total oxidation of nitrogen matter which changes nitrite to nitrate.
Assuming the chemical composition of nitrifiant bacteria is considerable in form of C5H7O2N. Therefore, utilizing one gram of ammonium needs 4.2 grams of oxygen to synthesize a new biomass which yields 0.13 grams of bacteria’s Journal of Engineering Science and Technology March 2009, Vol. 4(1) 74 M. A. Fulazzaky cells . During the period of nitrification, it seems that the oxidation of ammonium reduces the amount of alkalinity in the water wherein one gram of ammonium consumes 8.6 grams of alkalinity . Indeed, in the case of inadequate bicarbonate in a domestic wastewater, pH decreases. The biological process meanwhile produces the effluent with riches of nitrate identifying the passing of the effluent standards.
After the nitrification process is considerable stable identifying that the concentration of nitrate in the effluent is constant. The elimination of nitrogenous pollutants may be continued to change the reactor from aerobic to anaerobic condition so that, the nitrification process starts due to the presence of certain chemi-organotrope bacteria in the activated sludge which able to replace DO as sources of oxygen with the oxygen of nitrate and yielding free nitrogen as the final step of denitrification process. It is energetically remarked that the denitrification process is more effective than nitrification and, as a consequence, during the denitrification phase the growth rate of bacteria is more important so that this period is short.
The cycle of nitrification-denitrification is achieved by using the regulated timer which arranges at the switch-on to aerate and the switch-off to stop the aeration and vice versa and, when this cycle is correctly stable identifying that the global nitrogen is below 10 mgN/L which confirms to the effluent standards, we can continue to implement the chemical-biological phosphorus precipitation process.
The principle problem affects to the surface water caused by the presence of high concentration of phosphor is able to degrade the living environment which appears the rupture of ecological equilibrium in an aquatic ecosystem as the receiving media . Based on this factual it is necessary to remove the excess of phosphor that presents in wastewater.