Performance Assessment of the Rehabilitated Mudor Sewage Treatment Plant at James Town Accra-Ghana

The Rehabilitated Mudor sewage treatment plant at James Town was monitored over a period of 4 months (October 2017 to January 2018). This study analyzed the physical, chemical and biological parameters of the raw sewage and the treated effluent from the plant. The result indicates that the total removal efficiencies were 98.8%, 91.2%, 62.8%, 28.6%, 81.7%, 43.6%, 82.5% and 99.6% for BOD, COD, TSS, Nitrate-Nitrogen, Phosphate-Phosphorus, Ammonia-nitrogen, Sulphate and faecal coliform respectively. More than 13 parameters needed to be met according to the Ghana Environmental Protection Agency (EPA) guideline were satisfactorily met whiles ammonia, total suspended solids and phosphate were slightly out of range. From the results obtained, the overall performance of the rehabilitated plant was satisfactory and has seen some improvement with respect to the former recorded performance of the plant. With monitoring operation parameters for waste water plants discharge guidelines becoming stringent over the past years, it could be said that management of the Mudor rehabilitated treatment plant is on the right cause with full scale operation of the plant barely less than a year. Increase in the process steps through rehabilitation resulted in several significant improvements in effluent quality parameters.


Introduction
Environmental sanitation is an essential factor contributing to the health, prod-How to cite this paper: Ahmed, I., Ofori-Amanfo, D., Awuah, E. and Cobbold, F.  [4]. The loads are removed from waste water by screening and the grit removal chamber, this treatment process is termed as the primary treatment stage. Other processes of the plant includes; sludge thickeners, aerobic fixed growth reactors (trickling filter), which was formally two but upgraded to three, Final Settling Tanks and sludge drying beds. The flow from the above mentioned sewered areas are discharged into the plant inlet where foreign material load of the sewage is screened. The screened waste water is discharged into a receptacle where it is lifted to the fine screen chamber, where fine particles of sand are trapped. The grit and screenings end up in a waste chute which is cleared into a skip for disposal. The effluent from the grit channel is diverted to primary distribution boxes. The primary distribution boxes ensure an evenly proportion flow to the biological reactors. Each channel from the primary distribution boxes feed secondary and tertiary distribution boxes. The tertiary distribution boxes connect directly to the down pipes that convey waste water to the bottom of the UASB reactors. Anaerobic by-products, including methane (CH 4 ), carbon dioxide Journal of Water Resource and Protection reactors is collected into gas collector hoods to prevent release of biogas into the environment. The effluent from the UASB reactor flows by gravity to the trickling filters. Effluent from the trickling filters then flows to the Final settling tanks (FST) where fine solids are allowed to settle and further organic reduction is achieved before effluent flows to the final sampling chamber. Sludge collected at the FST basin is pumped back into the sludge thickeners. The drying beds receive sludge pumped from the sludge thickeners where liquid drainage is affected through sand filters and a system of under-drain.
The Mudor waste water treatment plant uses the Up-flow Anaerobic Sludge Blanket (UASB) reactor as a unit for sewage treatment ( Figure 1) and research has indicated that about 65% to 80% of organic matter removal efficiency can be obtained in conventional UASB reactors even with short retention time of about 4 to 6 hours in hot climate areas [2]. The process of the rehabilitation of the Mudor WWTP saw an extension in volume of treatment per day, extension of the trickling filters, and adoption of the activated sludge. The rehabilitation process consists of operational steps where microorganisms are grown with consequential degradation of particulate and dissolved liquid wastes. The  solids produced in these reactors are separated by process of sedimentation with most portion of the settled solids recycled back to the bioreactors so as to have high solids concentrations as well as rates of reaction ( Figure 1). Research works have also indicated that the distribution of the functions adopted in the rehabilitated operational process can vary within activated sludge due to seasonal flow rates variations, seasonal variability of biomass density and aeration conditions [5] [6]. Such variations have the potential to result in an operational risk impact on the plant and improper operation of WWTP may lead to discharge of contaminated effluents leading to negative consequences in relation to environmental and public health [7]. Research has also indicated that in developing countries 1.8 million people, mostly children, die every year as a result of water-related diseases [8] [9] [10]. Research has also outlined the major contribution to chemical contamination to have originated from domestic and industrial waste water discharges containing both organic and inorganic contaminants that negatively impact water quality [11] [12] [13]. Water quality is affected by a wide range of natural and anthropogenic influences [14]. Natural processes (hydrological, physical, chemical and biological) may affect the characteristics and concentration of chemical elements and compounds in freshwater. The works of Dione [14] also outlines factors such as human-induced point and nonpoint pollution sources being key contributors to anthropogenic impacts that affect water quality. These factors make it imperative for the performance of WWTP be monitored on a regular basis [6].
In this context as also highlighted by the works of Belhaj [7], this study therefore seeks to determine the overall performance of the rehabilitated Mudor waste water treatment plant at James Town, Accra; with specific objective of assessing the day to day operations and to determine the nutrient, organic and pathogenic removal efficiency of the rehabilitated plant. Exhaustive data from a previous research work [2] conducted on the plant before its rehabilitation was comparatively treated to ascertain the plant performance based on past observations of certain key product quality parameters. These results would not only give the managers of the plant a fair view of the effectiveness of the rehabilitation and operational management will and capabilities but also simplify design decisions to optimize pollutant removal from urban waste waters.
The plant was monitored by measuring the characteristics of the process parameters of both influent and effluents to assess the overall performance of the plant for sixteen weeks (four months). This paper presents an overview of the rehabilitated Mudor waste water treatment plant in the Greater Accra region of Ghana.

Study Area
The study was conducted at the rehabilitated Mudor waste water treatment plant

Sampling and Analysis Methods
Composite samples were made from each process unit daily. For each day, the Sampled (composite) waste water for the present research was selected from the various treatment units of the Mudor waste water treatment plant and process parameters analyzed, in terms of their COD which was measured after potassium dichromate digestion with HACH instrument (DR1900), BOD 5 test method APHA 5210, Total Suspended Solids [15], pH, EC and Dissolved Oxygen were measured using multi parameter pH meter (HQ40D LDO10101), faecal coliform, the nutrients (total nitrogen, ammonia nitrogen, phosphate, sulphate, nitrate) were determined using the HACH DR1900 in line with the APHA methods [15]. Details of the instrumentation make and models are highlighted in the electronic supporting document.

Qualitative Analysis of Process Influent and Effluent
The influents and effluents of the plant processes were analyzed for PH, dis-

Hydrogen-Ion Concentration (pH)
Most microbial life occurs within narrow pH range, it is typically evidence to be 6 -9. Biological treatment of waste water is of great concern in relation to the hydrogen ion concentration. Influent waste water with extremely high or low pH values are difficult/impossible to treat with biological means. Treatment plant effluent water with High or low pH ranges may affect the natural waters in the recipient as well [16] [17]. pH values recorded ranged from 6.74 -7.26 (Table 2), for the composite sample of the raw sewage. The analysis showed that the pH of the influent has a very narrow variety in both the acidic and alkaline range; the acidic nature of the influent could have been as a results of discharge from acid based compounds/chemicals, from SME/industries, homes that are linked to the treatment plant or discharged into open drains connecting into the treatment facility. The alkaline range of influent water, this is probably because of discharge from homes using detergents, soaps, creams etc. The close pH range values recorded indicates a less retention time for treatment as long as pH is not so severe to completely stop the bacterial metabolism generating CO 2 (acidic gas) as by-product. pH values of effluent from the UASB reactors ranged from 6.77 -7.82, maintaining almost a neutral range. PH values recorded ranges from 7.71 -8.09, 7.62 -8.32 and 7.88 -8.22 for the composite of effluent from the trickling filter, the final settling tanks and the final effluent discharged. Unlike the initial works that was done [2] which reported pH values of influent being higher than the final effluent even though it is within the range of 6 -9. It was seen in this work that measured pH values were consistently increased by between 0.3 and 0.9 units giving relatively stable daily, weekly and monthly average pH effluent I. Ahmed et al. Journal of Water Resource and Protection between 7.94 and 8.14 ( Table 2). This observation is consistent with the works of Belhaj and coworkers [7].

Temperature (˚C)
In order to maintain the optimal performance of full scale UASB plant or activated sludge plant, Solid Retention Time (SRT) should be changed with temperature in a dynamic way. The average temperature ranged recorded was 25.38˚C, 24.06˚C, 23.44˚C, 23.6˚C and 24.49˚C indicative of influent, effluent from the UASB reactors, effluent from the tricking filter, final settling tank effluent and the final effluent respectively, the plant can be classified as being operating at low temperature range of 20˚C -23˚C and or moderately high temperature thus less than 28˚C. This temperature range phenomenon is consistent with the previous work [2]. BOD 5 and nitrification are optimally achieved at given SRT with respective variation of days over maximum and low temperature ranges. Research work has indicated that high water temperature decreases the solubility gas and increases the photosynthetic rate of algae and aquatic plants. This phenomenon has the potential of leading to increased plant growth and algal blooms [18] [19]. It is also alerted that a general change in water temperature can affect the general health of aquatic organisms as organisms become stressed in too hot or too cold temperatures while their resistance to diseases and pollutants becomes lowered [18] [20]. The values recorded for each treatment units falls within the Ghana Environmental Protection Agency (EPA) permissible guideline and it is also in consonance with the work of Alabaster and Lloyd [21] which reported that natural inland waters in the tropics have temperature ranging between 25˚C and 35˚C.

Electrical Conductivity (EC)
The EC of water, like TDS, is an indicator of total salt content of the water [22].   Reduction in turbidity values is as a result of degrading of organic by microbial organisms in the waste water. Total solids values recorded ranged from 100 -1300 mg/l and 100 -400 mg/l for the composite of influent and final effluent respectively. The overall removal efficiency of the plant from the influent to the final effluent was 96.6% (Table 2) and this was also seen to be higher than that reported in the previous work [2] (Table 1).

Colour
Average colour recorded was 191.3 TCU for the final effluent discharge ( Table   2). The value obtained falls within the EPA acceptable limit of 200 TCU guidelines. Previous research conducted [2] did not report on such parameter. The initial average influent colour value recorded was 5389 TCU, colour being organic material that has dissolved into water, it could be said that most dissolved organic materials were reduced significantly by the various treatment units of the plant.

Dissolved Oxygen (DO)
Dissolved oxygen values ranged from 0.00 -0.28 mg/l and 1.02 -3.07 mg/l for the composite of influent and effluent respectively. UASB reactors recorded

Chemical Oxygen Demand (COD)
Composite samples of influent (raw sewage) and effluent COD from the UASB ported earlier [2]. Even though it meets the guideline, the overall removal efficiency of the plant was seen to be 91.2% (Table 2) which is lower than values recorded in the earlier work [2] as shown in Table 1 to be 94.4%. The decrease in the efficiency is attributed to the relatively low COD values of the influent that was received coupled with high variations between the minimum and the maximum recorded values during the study.

Biological Oxygen Demand (BOD)
Values within the EPA required regulation of 50 mg/l and this is consistent with the earlier work [2]. Even though, the obtained BOD values for the two research works meets the EPA guideline, the overall BOD removal efficiency of the plant in this work is 98.8% (Table 2) and is noted to be higher than values recorded by the previous work [2] which was stated to be 98.1% (Table 1).

Phosphate-Phosphorus
Taking note of This point of using it in irrigation was highlighted in the previous work as well.
However, the current management of the plant are using part of the effluent to water the lawns within the plant premises. On the other hand, research work conducted by Nthlumbi [23] indicates that high phosphate can stimulate a rapid growth of photosynthetic algae and cyanobacteria resulting in eutrophication.
Eutrophication also has the potential to increase treatment cost. It is not surprising that, work conducted by Akoto [24] shows that high level of phosphate in treated drinking water for a certain community in the suburb of Kumasi in Ghana has sewage as a potential source whiles Akpali [25] highlighted drains rich in detergents being the contributing factors of high phosphates.   Table 3).
Considering all the nutrients monitored, the effluent had nitrate to be very high in concentration followed by sulphate in all the samples monitored overtime and the nutrient concentrations were found to be in the order: This observed trend of nutrient in water where the anionic nutrients were found to be higher than ammonia is consistent with the work of Akoto [26] on treated drinking water except for phosphate that was lower. The various treatment units achieve a significant reduction in the faecal coliform

Conclusions
• The overall performance of the various treatment units after renovation of the treatment plant was satisfactory. • Almost all of the monitored physico-chemical and microbiological parameters met the Ghana EPA guidelines except ammonia-nitrogen, phosphate and suspended solids which exceeded the regulations guidelines.
• Final effluent discharge from the treatment plant into the Korle-Lagoon may not cause health risks or any environmental related problems.
• The plant performance is currently higher (after renovation) than the one reported in literature before the renovation.