Design of a Wastewater Treatment Plant for Paint Factories

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By Ndagire Gloria Linda*, Mulenga Steven, Dr Kinobe Joel

Ndagire Gloria Linda is a Co-Founder, Public Relations Director and Computer Aided Design Instructor at ZadeCAD Limited. She graduated with Bachelor of Science in Civil and Environmental Engineering from Uganda Christian University in 2019.

Corresponding Author: Ndagire Gloria Linda


In order to improve the health and livelihood of the public, there is a need to treat wastewater from the different sources which include municipal, agricultural and industrial areas. The main purpose of this project is to design a treatment system that could treat wastewater from Chromatic Paints Factory to dischargeable standards. Sampling was carried out at the factory, the quality of the wastewater was determined through conducting both in situ and laboratory tests, flow measurements using a bucket method. The jar test was also carried out to determine the optimum alum dosage in the wastewater. The different results from the tests were discussed in relation to the quality and the quantity of the wastewater generated. Therefore, the different objectives of the research and design project were met. This report provides an engineered design of the proposed treatment system which comprises the mixing unit, sedimentation tank, filtration unit. However, the company is advised to continuously monitor the quantity and composition of their wastewater in order to develop better informed design parameters such as flow rate. It is also recommended that a better sludge disposal method should be researched about.


The paper reports on a systematic process to investigate the quality and quantity of wastewater from Chromatic Paints Factory and design a system that treats it to discharge standards.

The study was guided by the following specific objectives.

a) Determining the wastewater characteristics and the volume of wastewater generated.

b) Determining the optimum dosage of alum to be used.

c) Designing a treatment system for the wastewater from Chromatic Paints Company.

Paint can also be referred to as a liquid solution composed of different pigments and solvents which is applied on different surfaces for decorative or protective purposes (Talbert, 2008). After continuous revolution and introduction of different raw materials especially the synthetic ones have posed a threat to the environment. Paint wastewater contains toxic compounds and was considered as inhibiting bacterial development (Fent, 1996). In addition to chemical treatment, an appropriate biological technology is required. The biggest problem at hand is poor disposal of paint and paint wastewater into the environment without treatment. This is the genesis of all paint wastewater problems because it introduces toxic waste into the environment.

Worldwide, different countries have come up and set regulations for the paint manufacturing industries and also minimum standards for effluent disposal into the environment. The paint industry is one of the most highly regulated industries in the world. So the producers have been forced to adopt low solvent and solventless technologies in the past 40 years and will continue to do so in the near future (International, 2017).

Almost all the surface and groundwater in Kampala City is polluted and the inhabitants of the city are highly exposed to health risks associated with water pollution. According to the Ministry of Health and KCCA, the recent outbreak of typhoid was partly due to polluted surface and groundwater (KCCA, 2016).

In addition to the above, an Industrial Wastewater Management Guide for Uganda provides that every paint factory/industry facility should have a wastewater treatment plant for effluent discharge to treat all the waste from the facility including that collected after washing and cleaning. pH adjustment, coagulation, aeration, sedimentation and disinfection are some of the processes that can be employed in paint wastewater treatment (KCCA, 2016).

Uganda is a developing country. This implies that more different infrastructure is yet to be set up or constructed. With increased construction, the demand for architectural coatings (paints) is increasing and has opened up new ventures of new paint manufacturing industries to join the business. This has also created a battle of paint in Uganda (Adengo, 2017).

1.1       Problem Statement

Chromatic Paints Factory lacked an efficient treatment system for its wastewater. This led to poor disposal of untreated wastewater into an underground pit (shown in Figure 1) and on land. According to Part 5(1) of the National Environment Regulation for Discharge of Effluent into water or onto land, every industry must have a treatment facility and a regulation of the amount of waste generated to standards that are not harmful to the environment (NEMA, 1999).

The current method used to manage the wastewater presents a big threat of leakages of wastewater into the surrounding environments including water channels and streams downhill which people depend. (Olayinka, 2015). Approximately 35% of the population around the world depend on different groundwater sources which are mostly from shallow aquifers to meet their water needs (UNEP, 2002), and this exposes people to the poisonous pollutants in this wastewater which includes heavy metal, eutrophication especially in water channels. Furthermore, some of the components of these wastes contain chemical elements which are likely to infiltrate and percolate into the subsurface environment upon discharge, and these subsequently accumulate into the soil pores (Idzelis, et al., 2006). The composition and quality of surface and groundwater has been declining due to the high increase in the industrialization and human activities (Kumar, et al., 2013). In addition, as paint wastewater flows as runoff into storm drains, the organic solvents and inorganic compounds are slowly broken down in water, depriving aquatic organisms of the oxygen they need to survive. The toxic nature of chemicals in solvent-based paints may also cause tumours to form in animals such as fish.

Figure 1: Showing the underground pit

This study was aimed at finding a solution to this problem by designing a treatment system for the factory through wastewater sampling, field and laboratory tests, analysis and design.

1.2       Justification

The paint factory does not have a proper effluent disposal management facility for its wastewater. This method of using an underground pit is not sustainable and efficient since in the long run it might affect the soil productivity and its concentrations, hence affecting the plant life (Jolly, et al., 2008). In addition to this, some inorganic waste is not decomposed by anaerobic processes/digestion, these pits are also ineffective at removing phosphorus and nitrogen compounds that have the potential to cause algal blooms in waterways in case there are leakages (Ground & America, 2008).

Despite the fact that there are regulatory bodies such as National Environment Management Authority (NEMA) in charge of ensuring proper wastewater disposal, Chromatic Paints company does not conform to these set regulations for effluent discharge.

Therefore, treatment of this waste water using an appropriate design in place, effluent will be treated before it is discharged, thus reducing the potential risk of contamination of underground water and land, hence protecting human and plant life.


This chapter outlines the research methodology that was used to conduct the research and inform the design. It consists of geographic scope and study methodology applied to achieve the objectives of this research.

2.1       Geographical and time scope

 Chromatic Paints Uganda Limited is located on Plot 5, Kasubi-Kawala, off Hoima Road in Kampala District.

Time scope: September 2018 to April 2019

2.2       Content scope

Investigation of the quality, quantity of the wastewater from Chromatic Paints Limited. Laboratory and field tests were carried out to determine the quality of the wastewater. The wastewater flow rate was also carried out to determine the quantity generated. The results from these tests informed the design of the wastewater treatment system.

2.2.1   Flow Rate measurements

The amount of wastewater produced was determined through measurement of wastewater flow at the factory. Flow varies from one day of the week to another month or season. Most of the wastewater was generated in the evening when there was cleaning of floors and mixing tanks, leading to high volumes of wastewater during that time.

The flowrate was determined using a bucket method (shown in Figure 2). The bucket method was chosen in preference to others because it is suitable for small flows and irregular channels and also due to the availability of the equipment required to carry out its procedure.

Figure 2: Determining the flow rate using the bucket method.

2.2.2   Field/in situ tests

 In order to assess the wastewater quality parameters, in situ measurements were taken at 2 sampling points for the preliminary tests, which were carried out on 20/12/2018.

Before the wastewater goes into the underground pit, it is first screened to reduce on the suspended solids. Hence sampled the wastewater both before and after screening.

The first sampling point was at the outlet point of the wastewater from the factory (before screening) and also the wastewater in the underground pit (after screening). This enabled the researcher to know the variations between wastewater parameters and those that needed improvement. These measurements were carried out between 4:00 – 5:00 pm with the help of a technician.

The parameters determined included temperature and dissolved oxygen. The above parameters were measured using a Mettler Toledo and a DO MRC.

At each sampling point, the measurement for each of the above parameters was conducted in triplicate.

2.2.3   Laboratory tests

The samples obtained  from the field were analysed for parameters such as colour, BOD5, COD, TSS, TKN, Total Phosphorus, Alkalinity, Sulphate. These tests were carried out to check whether the parameters of the wastewater are in relation to the NEMA standards of the effluent to be discharged to the environment.

 The jar test was carried out to determine the optimum coagulant dosage for clarifying the wastewater. All the laboratory tests were carried out at NWSC-Central Laboratory-Bugolobi.


After carrying out field and laboratory tests, the following results were obtained, represented and interpreted as shown below.

3.1       Wastewater quality characteristics

Table 1:  Showing the preliminary results of the wastewater from the factory.

The researcher carried out preliminary tests to determine the quality of the wastewater as shown in Table 1 and the parameters that needed to be improved.

Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Colour, Total Phosphorus (TP), total kjeldahl nitrogen (TKN), Total Suspended Solids (TSS), and Turbidity. All these were above the effluent discharge standards both before and after screening.

The high levels of BOD and COD were as a result of the different organics used in the manufacture of the paint, for example, titanium dioxide, calcium carbonate, magnesium silicate, cellulose (Gulin, et al., 2004). The colour was as a result of the organic material that has dissolved into solution, which leads to high values of the turbidity (Ibrahim & Gabr, 2014).

Alkalinity and Potential of Hydrogen (pH) were above the discharge standards before screening, and within the range after screening (Gulen, et al., 2006). This is because before screening, the wastewater is still rich in paint while after screening, some paint is taken off by the screen, hence the low pH.

Sulphate, lead, chromium were not detected. This is because these are water-based paints where water is used as a solvent. These paints have less traces of heavy metals.

Dissolved Oxygen (DO) was within the discharge range before screening, and out of range after screening. This is because after screening, the wastewater is stored in an underground pit which is always covered, hence limited oxygen supply (Metcalf & Eddy, 2003). Dissolved Oxygen is required in adequate amounts for survival of aquatic life and prevention of offensive odours. 

3.2 Wastewater flow rates from Chromatic Paints Factory

Below are the results obtained during both production days and days when cleaning activities took place (Saturdays).

DayFlow Rate (m3/day)
Monday (4th)135
Wednesday (13th)140
Friday (21st)130
Saturday (9th)180
Saturday (16th)190
Saturday (23rd)185
Average flow rate160
Table 2: Showing the varying flow rates

From Table 2, it is observed that during production days the flowrate was within the range of 130-140 m3/day while during Saturdays the flowrate was within the range of 180-190m3/day.

The peak flow rates were obtained during Saturdays when cleaning activities take place. Therefore, for proper design, calculated the average flow rate which was 160m3/day. This flow rate catered for both minimum and peak flow rates.

The flowrate measurements kept varying from day to day and time. This is because the factory works on a batch process where wastewater only flows when activities like production, cleaning are being carried out. Days from Monday to Friday are normal working days where more production of paint is carried out than cleaning activities. On such days, less is generated therefore leading to low values of flow rate.

Saturday is a day of general cleaning of the drums, flows, buckets. On this day more wastewater is generated, therefore leading to high/peak values of flow rate.

There was no constant flow rate, and therefore to enable proper design of the treatment system, calculated the average flow rate from the values obtained. Hence, Chromatic Paints Factory produces an average flow rate of 160m3/day of wastewater.

3.3       Determining the optimum dosage

Figure 3: A graph of turbidity against dosage of Alum

Figure 3 shows the average values of turbidity and dosage of alum. The jar test was carried out two times using the same dosages and the average of the results was taken.

A graph of turbidity against the dosage was plotted and appeared as above. From the graph, the optimum dosage is 300mg/L. This is the dosage which gives the least turbidity.

The jar test was carried out to determine the optimum coagulant dosage for clarifying the wastewater. The optimum dosage obtained was 300mg/L at a pH of 7.68. The pH of the wastewater kept increasing per dosage between the range of 7.5-7.8. The pH kept increasing because of the different salts used in the manufacture of paint for example calcium carbonate, magnesium silicate and their reaction with alum. Since the pH did not go above 7.8, that means it was still in the neutral range and therefore we did not need to adjust it (Philip, 2016).


The results from the tests carried out informed the design. A prototype or laboratory scale design was set up and the wastewater was run through the system as shown in Figure 4. The effluent from the system was tested and results obtained to determine its efficiency. The design was important in achieving the last specific objective.

Figure 4: Design prototype of the treatment unit for the paint factory

The wastewater had to flow from the mixing unit where we had agitation of the wastewater and alum, then to the sedimentation tank to enable settlement of the suspended solids. Lastly, to the filtration unit where we had adsorption of the contaminants by the Granular Activated Carbon (GAC).  The GAC was placed above the sand because it has a large surface area onto which the molecules can stick, and therefore enabling the adsorption process to take place (Summit, et al., 2015).

 The purpose of the sand being placed below the GAC was to trap other suspended solids that remained after sedimentation and also prevent breakthrough of flocs (EPA, 1995). The gravel worked as the base layer to support the filter media as recommended by (MWE, 2013).

4.1       Sampling of the prototype

In order to obtain the sample for effluent, the researcher used composite sampling method. The collected four individual samples (2 litres) at regular intervals after two hours during a 24-hour time span. Each individual sample was combined with the others in proportion to the rate of flow when the sample was collected. The mixture resulting from the composite sample formed a representative sample which was analysed.

 From the results of the influent and effluent, the researcher calculated the percentage removal of the system in order to determine the efficiency of the system.

Parameter% Removal
Table 3: Percentage removals for the different parameters

From all the calculations, the percentage removal for all the parameters was above 90% as seen in Table 3 and within the discharge standards, meaning that the system was efficient in treating the wastewater from Chromatic Paints Factory.

There was improvement in the water quality attributed to the presence of a sedimentation tank and filtration unit.

The sedimentation tanks allow settlement of solids, thereby reducing BOD and TSS since it enhances the removal of about 50-70% of TSS and 25-40% of BOD (Metcalf & Eddy, 2003). From this, we agree with a study carried out by (Metcalf & Eddy, 2003) since after sedimentation the water was clearer hence showing a reduction in colour, turbidity and hence BOD as shown in Figure 5. In addition, the reduction in colour is attributed to the flocculation as result of the addition of alum. The adsorption of the contaminants in the wastewater by the activated carbon helps in maximum removal of COD, TKN, colour, phosphorus (Peta, 2006). In addition to this, the filtering unit using activated carbon and sand also aided the retention of the suspended solids in the water thereby causing a reduction in the turbidity thus further reduction in the BOD.

Comparing this design to other designs used in treatment of water-based paints, for example; combination of a chemical coagulation/flocculation step with an aerobic biological process by (Souabi, et al., 2006) which removes 92% of COD, 97% of colour and 44.5% of BOD. From this, the proposed system is more efficient than the one of (Souabi, et al., 2006) because it has a higher percentage efficiency.

Figure 5: Showing the samples of wastewater from the mixing, sedimentation and filtration units

From the laboratory scale design (prototype), developed the actual design considerations and calculations of the treatment system as shown in Figure 6.

Figure 6: Cross sectional design, plan view of the treatment system

 5.0      CONCLUSION

The objectives of the project were met within the proposed time schedule. Releasing these loadings directly into the environment leads to a deterioration of land, water quality in the receiving environment.

The factory’s wastewater showed high levels of COD, BOD, TSS, colour, turbidity, TP and TKN. The system was able to treat the wastewater up to a percentage removal of above 90% for all of the parameters hence making the system efficient for treatment.

Chromatic Paints Factory produces approximately an average flow rate of 160 m3/day, and this was used in the designing the size of the sedimentation tank and other units. The optimum dosage of alum obtained from the jar test was 300mg/l.


It is also necessary to continuously monitor the quality of effluent from the treatment system in order to verify that its quality complies with the national discharge standards.

It is recommended that more research should be carried out in order to get the best way to dispose of the sludge to the environment.

It is recommended to carry out continuous measurements for the flow rate so as to obtain records of at least one year in order to develop an accurate peak to average flow rate factor.


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