Redesign of Anaerobic-Aerobic Biofilter for Domestic Wastewater Treatment Plant In Textile Industry

. One of the textile industries in Pasuruan already has a Domestic Wastewater Treatment Plant (WWTP) with a capacity of 35 m 3 /day. The treatment process combined physical, chemical, and biological processes using an anaerobic-aerobic biofilter. The domestic WWTP consists of a collection tank, equalization tank, anaerobic-aerobic biofilter tank, a filtration tank, and a chlorination tank. Existing conditions indicate that the domestic wastewater generated exceeds the capacity of the WWTP. Additional employees become one of the factors causing the increase in domestic wastewater discharge. Inadequate capacity has forced the company to bypass domestic waste into rivers. This biofilter was chosen because it could reduce high BOD values, have low operating costs, and operate efficiently. The anaerobic-aerobic biofilter reactor consists of a pre-settling tank, anaerobic tank, aerobic tank, and final settling tank. The evaluation results denoted that detention time in pre-settling, anaerobic, and settling units did not meet the design criteria. Thus, changing the design according to the design criteria . The redesign result of the anaerobic biofilter includes the pre-settling tank with a diameter of 2,5 m and a length of 3 m, an anaerobic tank with a diameter of 2,5 m and a length of 15 m, so that the total volume in the anaerobic reactor is 88.3 m 3 . Then anaerobic bath with a diameter of 2,5 m and a length of 6 m and a final settling tank with a diameter of 2,5 m and a length of 1,5 m so that the total volume in the aerobic biofilter reactor is 36,7 m 3 .


Introduction
Domestic wastewater is wastewater generated from daily human activities related to water use. Domestic wastewater is wastewater generated from household or industrial activities that have the potential to pollute water bodies and the environment [1]. This pollution is caused by the content of organic compounds, chemical compounds and pathogenic organisms in domestic wastewater [2]. The content of organic matter and fat can be a place for the growth of microorganisms, causing odor [3]. Domestic wastewater is grouped into two types: water and gray water. Blackwater comes from human waste, including waste from toilets or septic tanks. Meanwhile, gray water is produced from kitchen water waste containing oil and food residue and water from bathing and washing with soap and detergent [4]. Domestic wastewater must be treated to not pollute the environment and endanger the health of living things [5].
PT. X is a textile company with 1.755 employees. With a large number of employees, the higher the domestic wastewater produced so that PT. X has to require domestic WWTP so that in 2020 the construction of a domestic WWTP with a capacity of 35 m 3 /day. A domestic WWTP or domestic sewage treatment plant is a facility to treat wastewater generated from household activities or daily human activities [6]. However, WWTP development planning was carried out improperly. The addition of employees caused the amount of wastewater produced to exceed the installed domestic WWTP capacity, so wastewater treatment could be carried out non-optimally. It is evidenced by the high value of Total Coliform from treated wastewater. The coliform bacteria in waters allow for entering pathogenic and taxi genetic microorganisms that can affect the health of aquatic biota and even humans [7]. Coliform bacteria can cause digestive disorders and various diseases such as diarrhea, acute kidney failure, and meningitis in humans [8]. Therefore, it is necessary to make improvements to prevent environmental pollution by evaluating and redesigning Domestic WWTP following the amount of wastewater produced.

Research Method
This study was conducted at PT. X, which is located in Pasuruan Regency. The evaluation was carried out by testing the quality of domestic wastewater at the Graha Mutu Persada Laboratory with a sampling method that refers to SNI 6989.59:2008 method grab sampling at 4 points including the inlet, equalization tank, aerobic-anaerobic biofilter reactor and outlet. The wastewater quality test includes pollutant parameters such as pH, BOD, COD, TSS, Ammonia, Oil fat, and total coliform. After the wastewater quality test was carried out, an evaluation was carried out by calculating the removal efficiency of each unit compared to the design criteria of each Domestic WWTP unit for further calculations. Detailed Engineering Design for the aerobic anaerobic biofilter unit

Result
Domestic wastewater discharge was carried out by recording the value flowmeter installed at the inlet, and the outlet of the domestic WWTP value flowmeter was recorded by the officer at 07.00 A.M. every day. Based on the recording results, the average domestic wastewater discharge at PT. X is 62,7 m 3 .

WTP Unit Performance
An evaluation was carried out by calculating the Eligibility Efficiency of each WWTP unit with the following results: Based on the calculation results, it can be analyzed that the efficiency of removing organic pollutants in the collector and equalization tanks is quite high because the residence time in the collection tank is quite long. While the efficiency of the anaerobic-aerobic tub based on the calculation results is less effective than research conducted by Nasution (2008), the anaerobic-aerobic tub has an efficiency of 75-95% BOD removal, 80-85% COD, and 50-65% TSS [9]. Due to the short residence time, the process of decomposition of organic matter by microorganisms does not take place optimally. It is in line with the research conducted by Said (2006) [10]. Another influential factor is the absence of maintenance/cleaning in the aerobic-anaerobic reactor. Although the removal efficiency is insufficient, the results of the analysis of the quality of domestic wastewater for parameters BOD, COD, and TSS meet the government's quality standards. It is related to the content of organic matter in wastewater which is not too high. The cause of the low organic pollutants in domestic wastewater at PT. X includes a lot of wastewater that overflows and does not enter the treatment system, as well as the habit of employees in using excessive clean water

Redesign of Anaerobic
An anaerobic-aerobic biofilter is a biological treatment process with an inherent growth in which microorganisms were developed in a medium. This unit consists of several compartments, including an pre-settling tank to precipitate wastewater particles, an anaerobic tank to decompose wastewater with microorganisms, anaerobic tank to decompose wastewater with microorganisms with the help of aeration, and a final settling tank. The following is the result of the calculation of the performance analysis of the aerobic-anaerobic biofilter reactor in each compartment

Conclusion
Based on the evaluation results, the efficiency of removing organic loads in wastewater in aerobic-anaerobic biofilter reactors is less than optimal. The wastewater discharge exceeds the capacity of the existing WWTP, so it needs to be redesigned. The redesign of the anaerobic biofilter includes pre-settling tank with a diameter of 2,5 m and a length of 3 m, an anaerobic tank with a diameter of 2,5 m, and a length of 15 m so that the total volume in the anaerobic reactor is 88.3 m 3 . Then an aerobic tank with a diameter of 2,5 m and a length of 6 m and a final settling tank with a diameter of 2,5 m and a length of 1,5 m so that the total volume in the aerobic biofilter reactor is 36,7 m 3