Performance Analysis of Anaerobic Baffled Reactor and Constructed Wetland for Community Based Wastewater in Dar Es Salam, Tanzania

The treatment performance of community based (decentralized) wastewater treatment systems are not monitored by municipalities in Tanzania and therefore these systems pose pollution threat to receiving water bodies. The aim of this research is to assess and compare the treatment performance of existing community based technologies which are affordable, manageable and climate compatible in Tanzania. The selected existing decentralized technologies for this study were Anaerobic Baffled Reactor (ABR) found in Kigamboni, Dar es Salaam and Constructed Wetland (CW) found in Mbagala, Dar es Salaam. Wastewater samples in and out of these systems were collected and analyzed for physical, chemical and biological parameters. The observed average effluent concentration of BOD5 (67.5, 90 mg/L), NH3-N (276.6, 115.7 mg/L), PO4-P (13.2, 17.7 mg/L) and FC (9 x106, 4.2x106 counts/100mL) in ABR and CW, respectively testified to an inferior standard of treatment caused by mismanaged operation and maintenance. Both ABR and CW with slight adjustment were found to be effective in removal of all physical, chemical and biological parameters.


INTRODUCTION
Selection of a proper wastewater technology and infrastructure is a daunting challenge and continue to be a priority issues in developing countries especially in Tanzania. The wastewater management proposed for the new city of Kigamboni is the centralized model by using Membrane BioReactor (MBR) technology for wastewater treatment (Hakiardhi, 2012;URT, 2010). The proposed technology is widely used in developed countries but not in Africa. In Africa, MBR is only available in cape Town, South Africa and in Casablanca, Morocco (Judd, 2015;Singhirunnusorn, 2009). However, research shows that, for developing countries centralized, mechanical wastewater treatment options like MBR are not highly recommended, in some places many such plants have been neglected. As an example in Mexico more than 90% of the centralized systems were not functional (Flores et al., 2009). The reasons behind neglect the treatment plants were related to failure of government to provide necessary operation and maintenance requirement. The selected technologies were not sustainable, sustainability in this context is not only that, the technology should be economical but also, should be socially acceptable, feasible in term of technology and institutions, and be environmental acceptable (Singhirunnusorn, 2009). For the proposed eco-city of Kigamboni, there is a risk that, most operational cost, maintenance cost (material and equipment), energy cost will not be effectively expensed. Its common in developing countries that, decision makers tries to select expensive technologies, with a belief that, because technologies work better in developed countries, it will do it anywhere else. This is can be true, but most of such choices are not usually feasible in developing countries (Hophmayer-Tokich, 2006; Weichgrebe et al, 2008). The impacts of selecting a non-sustainable wastewater treatment technology spreads beyond its immediate time of operations, it affects the future generation as well (Massoud et al., 2009

2.1
Site location Wastewater sources for this study were collected from two sites. The first site is the Sludge Treatment Plant (STP) which is an anaerobic Decentralized wastewater treatment (DEWAT) plant run by UMAWA, the local community in Kigamboni area. The second site was the Constructed Wetland treatment at St. Anthony High school in Temeke district.

Experimental Methods
The Kigamboni Anaerobic Sludge Treatment Plant (STP -DEWATs system) found in Kigamboni comprise of biogas digester, Anaerobic Baffled Reactor (ABR) and it treats sewage collected from Pit Latrines and Septic Tanks ( Figure 1 and Figure 2). It was designed to serves about 5500 people. Before the plant had been constructed, the sewage had to be transported to municipal waste stabilization ponds for treatment. This plant also produces biogas energy which is used for cooking (Krzeminski et al., 2012). The project was constructed by the German organization called Bremen Overseas Research and Development Association (BORDA), and commissioned the plant to UMAWA, a community-based organization from Kigamboni. The sizing of the plant is as follows, biogas digester (settling tank 50m 3 , Anaerobic Baffled Reactors 12 m 3 , Sludge drying bed 50m 3 , and the French drain 8m 3 . As detailed in table 1, the plant is designed to treat 4.8m 3 /day, this is the sum total the black water and grey water amounting into 1.4 and 3.4 m 3 /day respectively. The designed BOD, Total Nitrogen and Total Phosphorus is 97, 19 and 3 mg/L, respectively. The designed flow rate is 0.7m 3 /h. Wastewater from pit latrines are poured into biogas settler to settle big particles and trapping the biogas produced (BORDA, 2016). Currently the system is hydraulically overloaded and there is uncontrolled infiltration of storm water into sewer manhole that leads to under performance of the system in treatment of wastewater.

Sampling and Analysis of Parameters
The influent and effluent wastewater samples were collected from the anaerobic Sludge Treatment Plant (STP) located in Kigamboni area for a period of four months. Other influent and effluent wastewater samples were collected from the Subsurface Flow Constructed Wetland System (SFCWS) for the same period. Wastewater samples were collected from influent and effluent of ABR and CW for the laboratory analysis twice per month for four months from November, 2015 to February, 2016 and the average values for each month were used in data analysis. Wastewater parameters analysed were physical (pH and temperature) Biological and Biochemical (Faecal coliforms (FC) and Biological Oxygen Demand (BOD5)) and chemical (Nitrate Nitrogen (NO3-N), Ammonia Nitrogen (NH3-N), and Phosphate Phosphorus (PO4-P)).
Physical parameters were analysed in situ using pH and conductivity meters. Chemical and biological parameters were analysed in Ardhi University Laboratory according to standard methods (APHA, 2012).

Performance of Decentralized Wastewater Treatment (DEWAT), A BORDA based anaerobic baffled reactor Sludge Treatment Plant (STP) found in Kigamboni
The results of pH in the influent of this ABR plant ranged from 7.45 -7.66 with an average of 7.55 while in the effluent ranged from 7.51 -8.18, with an average of 7.86 ( Table 2). Generally the performance of this plant met the required national wastewater discharge standards which require that pH of effluent treated wastewater to be between 6.5 and 8.5 (TBS, 2005). The temperature in the influent and effluent ranged from 22 -28 with an average of 25. The temperature and pH for the this plant is conducive for the microbial activities, they are within the accepted average of 25 ºC and 6.5 to 9 for pH according to (Balthazar, 2014;Metcalf & Eddy, 2004;Elyasi, 2015;Hann, 2015) The influent BOD concentration varied between 364 and 384mg/L with average of 374 mg/L. The average effluent BOD was 67.3mg/L which is above the designed effluent BOD for this DEWATS plant (40mg/L). These values will affect the plant uptake. On other hand, effluent results of NO3-N levers ranged from 1.4 to 1.95mg/L. This is a good result as it complies with the Tanzanian standards and even FAO recommend standard of a range 5-30mg/L. In theory, nitrification process is the one that, lead to higher values of NO3-N. However, values of Ammonia-Nitrogen recoded was higher in the effluent, this could be due to anaerobic nature of ABR, does not allow oxidation of NH4 to nitrite, and then to NO3, this could be the

Performance of constructed wetland at St. Anthony High school, Tanzania
Values for pH in the influent of this constructed wetland ranged from 7.18 -7.46 with an average of 7.3 ( Figure 3). While pH values in the effluent ranged from 7.15 -7.63, with an average of 7.4, these average pH results indicates that the variation in the influent and effluent is not significantly different. In terms of performance, this plant met the required national wastewater discharge standards which require that pH of treated wastewater effluent to be between 6.5 and 8.5 (TBS, 2005). The temperature in the influent and effluent ranged from 22.5 -27.5 with an average of 25 ( Figure 3). The temperature and pH for the this plant is conducive for the microbial activities, they are within the accepted range of 20-30 ºC and 6.5 to 9 for pH according to (Balthazar, 2014;Metcalf & Eddy, 2004;Kihila et al., 2014). Values for BOD concentration in the influent of this constructed wetland ranged from 76-420 mg/L with an average of 156.8mg/L. Meanwhile, BOD values in the effluent ranged from 42-260mg/L, with an average of 90mg/L. The removal efficiency is 42.6%. The BOD values for effluent and influent for this wetland is shown in Figure 4. The effluent BOD is supposed to be 30mg/L or below, to meet the allowable discharge standards (TBS, 2005). The higher BOD values in the effluents could be due to reason that the wetland is recently started to be operated and the wetland plants were still at early stage of growth during the time of the sample collection. This could mean that, there was no enough roots system for diffusing the oxygen from the plants to the wastewater (Sim, 2003). To improve the performance, close monitoring and compliance to the operation and maintenance requirement as stated in the operation manual, is required (Njau et al., 2010). The (NO3-N) values for effluent and influent for this wetland is shown in Figure 5. , however if an additional chlorination is added to this water, the result will lead to the good water that could be even allowed for other domestic uses. One of major source of the faecal contamination in the aquatic environment is the CONCLUSIONS In general, performance of this ABR plant was not producing good-quality of treated wastewater effluent. The reason for inadequate performance is that, wastewater and faecal sludge feed into the treatment plant is about 10-15 m 3 /day, this is up to three times higher than designed capacity, this ABR plant is designed for 4.8m 3 /day. The overloading is due to increase of number of household that, use this treatment plant, initially only 5500 people was using this but now up to 15000 people are use this plant, these people who mainly use pit latrines and septic tanks, prefer this ABR services instead of the municipal waste stabilization ponds for treatment, which is far and costly for them. Because of this, hydraulic overlaying resulted into poor removal performance of BOD and other parameters such as NH3-N, PO4-P, FC. Large amount of wastewater was not properly treated. The designed flow rate emptying or releasing wastewater the plant is 7m 3 /h. The operated flow rate was higher beyond its designed capacity; this is because the wastewaters are emptied at high speed from the tank to the treatment plant. Because of high speed of inflow rate at the influent chamber of the settling tank, it affects the performances of the Anaerobic Baffled Reactors (ABR), as wastewater does not settle in the active sludge and therefore not properly perform anaerobic treatment. In this plant, there are four ABR in series, so the wastewater retention time is shorter than expected. Also wastewater tends to bypass the horizontal sand filter, which is in the land chamber to polish the final effluent. To ensure discharging standards are met, this study, suggest that, wastewater and faecal sludge inputs have to be as per design. The efficiency of ABR will increase when the input of big quantities of water is loaded slowly in the digester. It is recommended that a pipe with small diameter be used to feed the digester. The performance for these CWs in removing pollutants is relatively low 6% -43% and this could be due to the reasons that, the wetland cell is still new (with an operation period of less than 1 year), wetland plants are still at early stage of growth and therefore there is insufficient oxygen released to the CW that lead to limited growth of aerobic bacteria who are responsible for aerobic decomposition of organic matters. However, literature concludes that, properly designed, operated and maintained constructed wetlands have high performance in removal of pollutants from wastewater, the performance in the removal of pollutants reaches up to 99.0% (Balthazar, 2014;Kimwaga et al., 2013). Both ABR and CWS with slight adjustment were found to be effective in removal of all physical, chemical and biological parameters.