Effectiveness of Sequencing Batch Biofilm Reactor Technology to Treat Domestic Wastewater in Basrah City

The efficiency of a Sequencing Batch Biofilm Reactor (SBBR) for domestic wastewater treatment in Basrah was assessed. The experiments were carried out via a laboratory-scale SBBR cylindrical vessel used for this study, with geometric volume of 26 L, having an internal diameter of 15 cm, a height of 40 cm, and a working volume of 13 L. After a one-month start-up cycle for biofilm growth on the fibrous filler, the SBBR research test period lasted two months. The SBBR was run for three weeks to ensure that the biological treatment systems were mature and those steady-state requirements were reached, throughout the starting-up phase of operation, the removal efficiency for COD, NH 3 -N, TN, and TP were 95%, 89%, 85%, and 93% respectively. The impact of aeration time on the SBBR efficiency was also tested by removal of COD, ammonia, total nitrogen TN, and total phosphorous TP under dif ferent levels of dissolved oxygen DO (2.0 – 6.8) mg\L. The SBBR method proved to be an effective method for treating domestic wastewater in Basrah city. The COD, NH 3 -N, TN, and TP concentrations in the effluent were 42, 6.7, 9.0, and 1.0 mg/L, respectively, with the removal efficiency rates of 90.32 %, 86.24 %, 84.75 %, and 84.38 %. When comparing the SBBR effluent value to the WHO, European, Iraqi, and Chinese discharge standards, it was observed that the COD concentration (42 mg/L) met these standards. while ammonia (6.7 mg/L), TN (9.0 mg/L), and TP (1.0 mg/L) met the WHO, European, and Chinese standard only.


INTRODUCTION
The sequencing batch biofilm reactor (SBBR), which alternates between anoxic and aerobic environments, is an effective method in removing phosphorus and nitrogen [Fu et al., 2010]. Furthermore, because of dissolved oxygen (DO) gradation throughout the aeration phase, in the internal part of the biofilm, SBBR provides an anoxic microzone [Choi et al., 2008]. There is a possibility to achieve a nitrification on the surface of biofilm and denitrification in the inner layers (simultaneous nitrification and denitrification (SND)) [Cassidy et al., 2000]. Therefore, SBBR has been used to eliminate (Phosphorus and Nitrogen) from different types of wastewaters simultaneously [Di Iaconi et al., 2004]. [Dulkadiroglu et al., 2005] found that the COD effluent had been in the range of 20-30 mg/l when SBBR was fed with domestic sewage at 400 mg/L COD, due to a stable amount of residual microbe products as part of the biological processing within the reactor. High COD removal efficiencies in the treatment of dairy sewage using SBBR at estimated organic loadings were performed [Abdulgader et al., 2009].
In order to obtain good removal efficiency, the reactor was continually aerated during the reaction process, as a result, the oxygen utilization rate (OUR) and consumption of energy are low. The Dissolved Oxygen concentrations and temperature are essential factors that influence the metabolic processes of microorganisms. The dissolved oxygen concentrations and temperature can an effect on the growth of nitrifying bacteria rate and actions [Andrade do Canto et al., 2008].
SBBR is already used in domestic wastewater treatment [Clifford et al., 2008, Sarti et al., 2007, dairy wastewater treatment [Zhan et al., 2006, Abdulgader et al., 2009], textile wastewater treatment [Park et al., 2010], tannery wastewater treatment [Di Iaconi et al., 2003], and for nutrient removal [Jin and Yao, 2012]. SBBR has a much higher pollutant removal performance than a traditional SBR [Singh and Srivastava, 2011]. Moreover, the possibility to enable wastewater denitrification in a (SBBR) by using an organic substrate in the form of acetic were investigated in addition to studying the characteristics of the sludge formed via SVBBR [Mielcarek et al., 2018, Kłodowska et al., 2018.
This study aimed to evaluate the effectiveness of SBBR in removing the pollutants via a laboratory-scale SBBR and compare the effluent with various international discharge standards. Figure 1 illustrates the laboratory-scale SBBR cylindrical vessel used in this study, geometric volume is 26 L with an internal diameter of 15 cm, a height of 40 cm, and a volume of working is 13 L. The SBBR was fabricated with transparent plastic, 4 mm thick material in order to observe biofilm and sludge in the reactor easily. In order to improve the mixture in the reaction phase, the feeds were added into the reactor from the bottom. Plastic units of fibrous filler were hung in the reactor, which measures 30 cm in length and has over a thousand fiber strands. There were many filaments scattered to create a wide surface area, and flexible fibers yarns swing with the wastewater in the SBBR reactor during aeration to boost mass transfer in the biofilm. During the acclimatization period, the 24hour operating cycle included approximately a thirty-minute filling period. The reactor was supplied with air via an air pump, the aeration air diffusers were placed on top of the settling region to allow large particles disconnected from the biofilm to settles during the aeration process.

MATERIALS AND METHODS
As a seeding material for the reactor, activated sludge was collected from a local municipal wastewater treatment plant. The operation of reactor procedures, such as feed, aerate, settle, and withdraw, were all monitored by timers. A cap was set over the reactor, but it was not sealed. The aerobic and anaerobic intermittent environment was set up by an air compressor. Normally, the status of microbes in the SBBR is affected by biofilm carrier, which is a critical parameter for the successful starting up of a reactor. Although the biofilm supports bacteria attachment, it also acts as a filter that prevents suspended solids (SS) and other contaminants from entering the treated water. As a result, the SS contents in the effluent in this SBBR system may be less than 0.5 mg/L, which is better than in conventional SBBR systems [Dinçer and Kargi, 2001].

Experimental Conditions
The wastewater in this research was collected from the discharge point of the manhole for many houses in the Abo al-Khaseeb area in Basrah city south of Iraq. As shown in table 1, the main characteristics of the sewage constituents used in this study were compared with universal concentrations of domestic wastewater.
With parameters such as BOD, COD, TP, and TSS, it is clear that raw Basrah sewage is of medium strength. Raw Basrah sewage, on the other hand, has high strength with parameters like ammonia, TN, and TDS. The TDS levels were high due to increased salinity in Basrah water supply. The homes in Basrah city use septic tank systems to treat their wastewater on-site. When a septic tank is not properly maintained, high levels of nitrogen (Ammonia and TN) can be released into the sewage system.
During the time of acclimatization, Initially, in the reactor, 6 L of activated sludge is seeded with no additions, and the air was provided by diffusers, and the Dissolved Oxygen (DO) concentration is kept above 3.0 mg/L within the aerobic process for biofilm maturation, [Rusten et al., 2006]. In order to maintain the biofilm under suitable conditions, a minimum concentration of DO equal to 3 mg O 2 /L was maintained in the SBBR reactor. The volume of exchange was set at 50 percent, and the temperature was controlled around 25-35°C in the experimental processes to sustain the high efficiency of microorganisms, which have a significant impact on their respiratory rate.

Start-up Reactor and operation
During the start-up phase, SBBR is operation at 12/24 h cycle times during a day that is composed of wastewater (fill 0.5 hr., anaerobic time 3.0 hr., aerobic time 8.0 hr., settle 1.0 hr., and discharge 0.5 hr.), a total of 12 hours. After a one-month start-up cycle for the biofilm growth on the fibrous filler, the SBBR research test period lasted two months. SBBR was run for approximately one month to ensure that the biological treatment systems were mature and that the start-up requirements were reached.

COD variations within the period of start-up
At the beginning stage during the start-up cycle, SBBR reduced up to 35 percent of COD, and the effluent concentrations were decreased by

TN variations within the period of start-up
The Total Nitrogen (TN) variations in SBBR are shown in figure 4. In the SBBR reactor, TN had some changes when compared to the COD trend. After one week, the TN levels in the reactor have dropped from 51 mg/L to 9.8 mg/L, indicating the removal efficiency of TN is high. The Total Nitrogen concentration tended to rise as domestication time progressed, but then gradually decreased to about 8.0 mg/L.

TP variations within the period of start-up
The Total Phosphorus (TP) concentration was reduced from 6 mg/L to 1.3 mg/L within the first two days., as shown in Figure 5.
However, on the fifth day, the total phosphorus concentration effluent in the SBBR reactor was raised to 3.2 mg/L; afterward, the total about less than 280 mg/L, as clear in Figure 2. The removal efficiency of COD was steadily increased as the acclimation period was extended after two weeks, with a stability efficiency of 85 -95 percent and an average effluent COD concentration of 36 mg/L. During the entire start-up phase, the COD removal efficiency in the reactor was nearly 95.0 percent, indicating that the reactor had achieved a successful start-up for COD removal.

NH 3 -N variations within the period of start-up
The variance of NH 3 -N was close to that of TN, as seen in Figures (3 and 4), and the NH 3 -N effluent concentration is varied clearly. The amount of ammonia nitrogen was steadily degraded firstly, probably due to the poor metabolism of Ammonia Oxidizing Bacteria. The NH 3 -N effluent concentration then decreased from 44 mg/L to 5 mg/L, meaning that the reactor was efficient in the removal of nitrogen.

SBBR System in Normal Operation to Remove Different Pollutants
It is possible to divide the operation of SBBR into two conditions, start-up and steady-state. The system of SBBR was worked in the start-up condition before the steady-state condition. When the removal of the rate of COD, NH 3 -N, TN, and TP could be consistently held at 95 %, 89 %, 85 %, and 93 %, respectively, this indicates to the steadystate condition is reached. As shown in Table 2, the SBBR process was performed at steady-state in three different cycle operation modes, referred to as 1st, 2nd, and 3rd cycle modes.
Every SBBR operation cycle mode is consisted of the fill, react and draw phases. The react time for any cycle mode was the total cycle excluded the times for the fill and draw, within two months   of operation and acclimatization, the SBBR had reached a steady state. The average results of the third operation cycle mode for the SBBR system will be discussed in the sections below. The COD, NH 3 -N, TP, and TN effluent concentrations were measured within the 3rd operation cycle mode for 8 hours of aeration in order to evaluate a more suitable aerobic period. The concentration of DO was recorded between 2.0 and 4.9 mg/L. The concentration of COD dropped significantly in the first two hours of the aerobic process, reaching 299 mg/L, as shown in Figure 6. After 8 hours, the COD concentration has decreased to 42 mg/L. The concentration of NH 3 -N dropped significantly and reached 16.36 mg/L after 6 hours, meaning that the nitrifying bacteria were active.
Since the conversion of NH 3 -N to NO 3 and NO 2 , the concentration of Total Nitrogen did not change rapidly at the beginning. After 5 hours, the TN concentration had dropped slightly, and after 7 hours, it had dropped to 15 mg/L Figure 7. The concentration of NH 3 -N gradually decreased simultaneously, indicating that nitrification and denitrification were occurring at a similar time at this phase.
In the early aerobic stages, the TP concentration dropped quickly, indicating that the polyhydroxy butyrate (PHB) accumulated in the body has been completely oxidized.
As shown in Figure 8 after 5 hours, in the SBBR system, the Total Phosphorus concentration had stabilized at 2.25 mg/L, indicating that the phosphorus removal process had been accomplished. Aeration  for a long time causes the bacteria to produce more PHB, which reduces their ability to remove phosphorus [Metcalf et al., 2003]. In the SBBR system, the 8 hours aerobic period is preferable due to the varying times for different reaction processes.

Evaluation of the SBBR Performance
Two approaches have been followed to investigate the performance of biological treatment by the SBBR system as below:

Comparing with other SBBR Studies
The removal efficiency of present SBBR research was compared with the removal efficiencies of other SBBR studies is shown in Table 3. Some researchers examined how contaminants were removed in a smart, monitored SBBR for domestic sewage treatment.
The COD removal efficiency of this study was closer to that of [Ding, et al., 2011;Wang, et al., 2015 andCai, et al., 2013], while is far from a study by . The ammonia removal efficiency in the current study was the closest to that of [Wang, et al., 2015;Ding et al., 2011], and . The TN removal efficiency in the current study was closest to that of research by . The TP removal efficiency of the present study was not close to any removal efficiencies results of studies in Table 3.

CONCLUSIONS
1. In this research, the SBBR system has been used for domestic sewage treatment. The SBBR operation method has three cycle modes (first, second, and third). The following conclusions can be drawn from the tests and results conducted in the current study: 2. When the sewage characteristics of Basrah were compared to the typical characteristics of untreated domestic wastewater, BOD (210 mg/L), COD (430 mg/L), TP (6.5 mg/L), and TSS (270 mg/L) were considered to be in the medium strength range, while Ammonia (48 mg/L) and TN (58 mg/L) were found to be in the strong range. 3. The SBBR method proved to be effective in treating domestic wastewater in Basrah city. COD, NH 3 -N, TN, and TP concentrations in the effluent were 42, 6.7, 9.0, and 1.0 mg/L, respectively, with the removal efficiency rates of 90.32 percent, 86.24 percent, 84.75 percent, and 84.38 percent. 4. The effects of aeration time on the efficiency of the SBBR were also studied in terms of removal chemical oxygen demand (COD), ammonia, total nitrogen TN, and total phosphorous TP under different levels of dissolved oxygen DO (2.0 -6.8) mg/L. 5. When comparing the SBBR effluent value to the WHO, European, and Chinese discharge standards, it was observed that the COD concentration (42 mg/L) met these standards. while ammonia (6.7 mg/L), TN (9.0 mg/L), and TP (1.0 mg/L) met the WHO, European, and Chinese standard only.
The SBBR efficiency was investigated in this study, and it performed well as a suitable biological treatment method for the treatment of domestic wastewater from Basrah.