Optimization of coagulation and flocculation in concrete wastewater of precast industry

Received 09-02-2021 Revised 09-03-2021 Accepted 30-03-2021 Available online 30-03-2021 Abstract. The The population increase until the end of 2019 reached 267 million. This is in line with developments that support activities. This is inseparable from the actions of one of the precast concrete companies PT.WB Precast Plant Karawang in supporting development that produces waste in the form of wastewater. The parameter measured as a reference in carrying out processing is the Minister of Health Regulation Number 32 of 2017. This study's method refers to turbidity as a physical parameter, namely 25NTU and hardness total as a chemical parameter, which is 500 mg / l. CaCO3. Objectives: The purpose of this study was to determine the optimization of the use of PAC as a coagulant and flocculant to reduce the turbidity and total hardness and determine the optimum detention time of flocculation. Method and results: The sampling method in this study is observation with the data collection method is descriptive. The population in this study is concrete wastewater with parameter values that are not in accordance with the standard. Conclusion: By using PAC 10% the optimum doses is 140 ppm, and the optimum detention time of flocculation is 5 minute that can reduce the turbidity from 275 NTU to be 11.615 NTU or 95.7% and can reduce total hardness from 948.75 mg/l CaCO3 to be 491.25 mg/l CaCO3 or 48.2%. Keywords


Introduction
The population in Indonesia until the end of 2019 reached 267 million people [1].
This made development inevitable. The construction industry is a significant sector for increasing economic growth. Economic activity in almost all countries is closely related to the construction industry [2]. Furthermore, all developments also generate residual content from the activity which is called waste and is a serious problems [3]. If the waste produced is not properly managed, it will interfere with activities in the construction project itself and the environment around the project [4].
Construction with various wasteful factors makes people think of creating innovations, one of which is precast concrete technology to make development more practical, convenient and save time. One of the precast concrete providers is PT. WB Precast. With a production capacity of up to 575,000 tons / year [5], companies need to participate in waste management and environmental protection.
Adequate management system to minimize negative impacts on the environment from industrial activities [6]. Improving the quality of industrial wastewater will have a positive impact by improving the quality of wastewater in the area, which will increase customer, government and banking confidence in supporting economic conditions and industrial business [7].
Waste at PT. WB Precast produced is a type in the form of wastewater which is the result of the activities of the spinning spun pile process, washing the batching plant and truck mixer [5]. In the regulation of the Minister of Health, Number 32 of 2017 (3), regulates water quality from physical parameters, namely turbidity with a maximum value of 25 NTU and chemical parameters, namely hardness with a maximum value of 500 mg/l CaCO3 [8]. Meanwhile, the waste here does not undergo a treatment process that is able to comply with the standards before the waste is disposed of into the water body. This is a problem for both the company and for the environment as the water body is in the process of Accelerating Control of Pollution and Damage to the Citarum Watershed (DAS) with its main program known as the 'Harum Citarum Program' as outlined in Presidential Regulation No.

15/2018 signed by the President Indonesia
The water purification process is carried out using Poly Aluminum Chloride (PAC) because it is good for reducing water turbidity and waste in binding impurities in the form of sludge [9] . The dosing of chemicals must be in accordance with the conditions of the water to suit the needs [10].
In addition to providing the appropriate doses, optimization of the slow mixing detention time is also carried out to save energy while still providing results according to needs. Therefore, the dosing of chemicals and the flocculation detention time must be efficient and produce clean water products that apply to the standard.

Objectives
For this study, the objectives are carried out to determine the key parameter of concrete wastewater, determine the optimum doses of PAC 10% and detention time of flocculation slow mixing.

Problem Limitation
For this study to remain in focus, namely with the desired objective, the writer sets the following restrictions as scope and limitation. The scopes of this study are the sample were taken during May 2020 -June 2020 from PT. WB Precast Plant Karawang, and Coagulant and Flocculant using PAC10% from PT. Pantai Masand parameter that measured are turbidity and total hardness. The limitation of this study is the turbidity of the wastewater range for research is 270 NTU to 380 NTU, while the hardness ranges from 840 to 1080 mg/l CaCO3 that was concrete wastewater from the spinning spun piles process, the washing of the batching plant, and the truck mixer process.

Data Collection Method
The sampling method in this study is observation. The population in this study is concrete wastewater. The samples taken were conducted by May 2020 -June 2020 at PT. Precast Plant Karawang. The sample used in this study is wastewater from the spinning spun pile process, washing batching plants and truck mixers. Ensure the company has production, and the weather conditions are not raining so that the character of the wastewater samples taken is almost the same. Check the turbidity and hardness of the sample before starting the experiment to get initian values.

Tools
The tools used in this study include jar test, beaker glass 1000 ml, bulb, pipette 5 ml, volumetric pipette 10 ml, volumetric flask 50 ml, volumetric flask 100 ml, measuring glass 250 ml, beaker glass 1000 ml, wash bottle, Eutech TN-100 Handheld Infrared Turbidity meter and Hanna Instrument 3812 Test-kit total hardness.

Materials
The materials used in this study include wastewater samples, 10% PAC solution, and aquadest.

Sampling Preparation
The sample used in this study is wastewater from the spinning spun pile process, washing batching plants and truck mixers, where the wastewater has passed the cement sludge deposition process in the settling tank. Ensure the company has production, and the weather conditions are not raining so that the character of the wastewater samples taken is almost the same. Check the turbidity and hardness of the sample before starting the experiment to get initial values.

Jar Test
Jar Test is a method used to determine the effectiveness of adding coagulants and flocculants to water purification processes. So it can determine the optimum amount in addition of PAC10% as a coagulant and flocculant and optimum of flocculation detention time.

Measurement of Turbidity
The working principle of turbidity is the measurement of water turbidity in the presence of the influence of the intensity of the transmitted light. When the light beam hits the scattering particle medium, most of the light will be transmitted and part of the light will be scattered in all directions randomly by these particles [11].
Measurements were made using the Eutech TN-100 Handheld Infrared Turbidity meter.

Measurement of Total Hardness
Measurements were made using the Hanna Instrument 3812 test-kit with hardness checking capabilities ranging from 0 to 300mg / L CaCO3. Regarding clean water quality requirements, the maximum permissible hardness level is 500 mg / L. Therefore, samples that have been given the concentration need to be dissolved up to 10 times. After do the titration, read off the millilitre of titration solution from the syringe scale. Total hardness = a ml x 10 dellution x 300 (mg/L CaCO3)

Measurement Flocculation Detention Time
In determining the optimum flocculation detention time, determine the optimum dose to be used and then vary the stirring time, namely 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes and 10 minutes.

Result
Based on the results of research conducted using water samples at PT. WB Precast, data as many as 7 samples of wastewater taken at the same place, namely after passing through the sedimentation basin ensuring that there is production and the weather is not raining.
Overall, it can be seen that the addition of PAC to the wastewater samples

Doses of PAC
PAC has a substantial impact on the remediation of the city's black and odorous river sediments and overlying water [12].Poly Aluminium Chloride (PAC) accumulates at high concentrations in the waste activated sludge [13]. Poly Aluminium Chloride (PAC) as a coagulant in the water purification process has been carried out on a laboratory scale to determine the performance of this PAC [14]. However, because in the process, PAC can form flocc well, it functions as a flocculant to save on chemical use.

3.1.1.1Turbidity
Turbidity is a physical parameter that is measured to determine the effectiveness of the coagulation-flocculation process. The turbidity can be seen in figure 1. In Table 1, a graph of the change in turbidity can be seen after adding PAC. This

Total Hardness
Total hardness is a chemical parameter that is measured to determine the effectiveness of the coagulation-flocculation process. The total hardness value can be seen in figure 2. In

Flocculation Detention Time
In the slow mixing of flocculation, the speed is 60 rpm for detention time is 10 minutes. The wastewater is then allowed to settle for 30 minutes to precipitate the formed floc [15]. The parameters are measured to determine the effectiveness of the coagulation and flocculation processes. This is done to get the optimum value for mixing. Slow mixing needs to be calculated to find the most efficient time. In this experiment, slow stirring was performed at 60 rpm starting from 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes.
a. Turbidity Based on the graph of Table 4

Discussion
Based on experiment, after varying the dose of 100 ppm to 150 ppm, turbidity can reach the standard since the dose of 100 ppm. However, at total hardness, turbidity can reach the standard from a dose of 140 ppm. Therefore, the optimum dose is 140 ppm so that both parameters can reach the value according to the standard.
The settling time velocity of each sand particle is 10,361 m / s and the mud is 0.0016 m / s [16]. This is the reason the flocculant detention time is 8 minutes or faster, because the liquid waste from the concrete industry has relatively high suspended solids because it comes from sand so that it is easier to settle and form floc, compared to colloids such as mud from river water.

Conclusions
The key parameters of concrete wastewater are turbidity and total hardness.

Recommendation
The recommendation in this study is the planning of the dimensions of waste processing on a lab scale made on an industrial scale and there will be further research on the use of PAC10% in the coagulation and flocculation process in the concrete industrial wastewater.

Acknowledgments
In the preparation of this paper, the support from various parties is closely related.
The author is especially grateful to all those who have helped. Many researchers receive guidance, guidance and assistance as well as encouragement from various parties, both moral and material. On this opportunity, the author would like to thank profusely to: God, with all His graces and gifts who provide strength for researchers in completing this thesis. To Mrs. Temmy Wikaningrum, M.Si. As a supervisor who always provides guidance, direction, encouragement, and enthusiasm to researchers, this paper can be completed. All lecturers and all academic staff who always help provide laboratory facilities to researchers so that they can support the completion of this thesis. To the PT. WB Precast which is willing to be used as a case study in this research, especially to Gede Wiryanata who helped in the sampling Process. And many other parties were very influential in this writing process Hopefully, this research can be useful for researchers in general to readers.