Engineering and Technology Journal e-ISSN: 2456-3358 Volume 08 Issue 05 May-2023, Page No.-2207-2212 DOI: 10.47191/etj/v8i5.07, I.F. – 7.136 © 2023, ETJ 2207 Nyoman Sri Widari, ETJ Volume 08 Issue 05 May 2023 The Effect of Starter Ratio on Tofu-processing Wastewater Fermentation into Fertilizer Agung Rasmito 1 , Abas Sato 2 , Nyoman Sri Widari 3 1,2 WR Supratman University, Departement of Engineering. Arief Rachman Hakim 14, Surabaya, Indonesia 3 Katolik Darma Cendika University, Departement of Engineering.Dr. Ir. H. Soekarno 201, Surabaya, Indonesia ABSTRACT: The process of tofu manufacturing produces solid (slurry) and liquid wastes with high protein content. Tofu- processing Wastewater can be used as the primary material for liquid NPK fertilizer production. The process of converting tofu- processing wastewater into liquid fertilizer was simple and requires a short fermentation time. The fermentation process was carried out by mixing of EM 4 (starter for fermentation liquid), alcohol as solvent and organics matter. The selection of organic matter that is used as the primary ingredient of liquid fertilizer would affect the content of N, P and K substances in the product. Banana peel and cabbage are organic matter with a high calcium and phosphorus content. This research was conducted to determine the effect of the addition ratio of cabbage and banana peel to time duration of fermentation on the tofu- wastewater processing into liquid fertilizer. The results showed that increasing the ratio of cabbage to the starter increased the levels of N and P along with the length of fermentation time. However, increasing the cabbage ratio in the starter causes a decrease of K in liquid fertilizer. KEYWORDS: Tofu wastewater, fertilizer, fermentation I. INTRODUCTION Tofu is a source of vegetable protein for the people of Indonesia. The process of making tofu is done by mixing soybean essence with vinegar. This process causes the protein to coagulate and become denser when pressed [1]. The solid waste generated from making tofu is in the form of wet dregs (pulp) with a fairly high protein content of 23.5% [2]. The solid waste generated in this process can be used as secondary products such as "tempe gembus," animal feed, and processed into crackers, shredded, and dry bread [3]. However, solid waste processing must be done quickly because tofu dregs rotten rapidly. The soybean-based tofu-making industry produces liquid waste that has the potential to pollute the environment and is one of the industries that produces organic liquid waste [4]. The chemical content of the liquid waste from the tofu manufacturing process contains Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), and high pH (acidity). Tofu- processing Wastewater has a BOD of 5643-6870 mg/l (standard 300 mg/l) and a COD content of 6870-10,500 mg/l (standard COD 600 mg/l) [5]. These substances can pollute the environment and produce a very pungent odor. Water pollution can also kill aquatic organisms, cause disease, and become a breeding ground for mosquitoes [6]. The wastewater treatment process can be carried out using wastewater treatment technology or an Oxidation Reactor [7]. However, the technology is expensive and complicated to be applied in the small household industry [8]. The wastewater purification process can be carried out by filtration-absorber process using vetiver grass and zeliac [9] or coagulation – filtration using Polyaluminum Chloride (PAC) – Active filtration matter (quartz, activated carbon, and zeolite) [10]. However, the process of handling tofu- processing water waste using filtration is considered less effective because it still has noticeable content of BOD and COD beyond the water quality standard and takes a long time [6, 9–11]. Several studies were conducted to increase the economic value of tofu-processing wastewater by processing the waste into biogas [12] and liquid fertilizer [13]. The Anaerobic Digestion process in biogas processing produces gas and liquid that can be used as fuel. The residual sludge from biogas processing can cause soil contamination and water eutrophication if released directly into the environment. Biogas slurry contains high content of organics matter (79– 11480 mg/L), nitrogen (~111–3691 mg/L) and phosphorus (11–95 mg/L). Biogas Slurry can be reprocessed into liquid fertilizer [14]. Tofu processing water waste also has a high level of NH3, so it can be fermented into a component of NPK fertilizer [15]. Converting tofu-processing wastewater into liquid fertilizer is simple and requires a short fermentation time. The fermentation process is carried out by adding EM 4 (fermentation liquid), alcohol solvent and organic matter. Alcohol solvent is added as an antiseptic [16]. The fermented tofu-processing wastewater can be directly applied to plants. Liquid fermentation of tofu-processing wastewater and AB