1 st International Conference Eco-Innovation in Science, Engineering, and Technology Volume 2020 http://dx.doi.org/10.11594/nstp.2020.0512 How to cite: Kurniasari, L., Safrilia, S., Ramadhany, N. M. M. F., Ramadhan, I., & Hidayah, E. N. (2020). Performance of spirulina platensis in oxidation ditch reactor for treating tufo wastewater. 1 st International Conference Eco-Innovation in Science, Engineering, and Technology. NST Proceedings. pages 86-90. doi: 10.11594/ nstp.2020.0512 Conference Paper Performance of Spirulina Platensis in Oxidation Ditch Reactor for treating Tofu Wastewater Lolita Kurniasari 1 *, Savira Safrilia 1 , Ni Made Maya Febriana Ramadhany 2 , Iqbal Ramadhan 1 , Euis Nurul Hidayah 1 1 Undergraduate Program of Environmental Engineering, Universitas Pembangunan Nasional “Veteran” Surabaya, East Java, Indonesia 2 Master Program of Environmental Science, Universitas Pembangunan Nasional “Veteran” Surabaya, East Java, Indonesia *Corresponding author: ABSTRACT Spirulina platensis is a type of blue - green algae that has a micro-sized spiral shape and lives in marine waters. There are so many benefits of this microalgae, one of which is it can degrade organic pollutants in wastewater. Excessive nitrate and phosphate in the water can cause eutrophication which is indicated by the death of many sea biotas because of phytoplankton bloom. In this research, tofu which high in organic pollutants are used as experimental test media. The microalgae which will be tested is cultivated first to obtain a sufficient amount for research, then the microalgae are acclimatized before being put into an Oxidation Ditch Reactor mixed with tofu waste with a capacity of 250 liters, ran with 60 rpm brush aerator for 7 x 24 hours and also uses natural lighting from sunlight. samples were taken once a day at 12 noon each day. This research has a variety of wastewater: algae that are 1:1. From the results, it can be observed that Spirulina platen- sis microalgae could reduce maximum phosphate by 33,15 %, from 18,1 mg/L to 12,1 mg/. Furthermore, microalgae also capable of decreasing ni- trates by 46,07 from 0,89 mg/L to 0,48 mg/L. Keywords: nitrate, oxidation ditch algae reactor, phosphate, tufo wastewater E-mail: lolitakurniasari@gmail.com Introduction Nitrates and phosphates are a source of nutrients needed by living organisms in the waters. But if these nutrients are in excess and cross the threshold, eutrophication will occur which disturbs the ecological balance of organisms in the water (Boeykens et al., 2017). In addition, if you consume drinking water that is high in nitrate content, it will cause methemoglobinemia in infants, liver damage, and even carcinogenic diseases (Fewtrell, 2004).Therefore, removal of nitrates and phosphates in water is very important to improve water quality. At present, various types of treatment are applied to degrade nitrates and phosphates (Yama- shita et al., 2014). But microalgae-based biological treatment is the most interesting because it has a high efficiency and low cost. In addition, if processing with microalgae, no more waste is released by the microalgae. Spirulina platensis is used because it can reduce the nitrate content in water only at relatively low concentrations (Nemcic-Jurec & Jazbec, 2016). Spirulina platensis is a green- blue microalgae that has a spiral length of 43 - 57 µm and a width of 26 - 36 µm (Jung & Kruger- Genge, 2019). Spirulina has several advantages over other types of microalgae, namely it is faster in production and its biomass is easy to harvest (Soni & Sudhakar, 2017). The oxidation ditch is a modification of the activated sludge process which has been known for many years to remove nitrogen content (Hadisoebroto et al., 2014). This building is usually made of concrete or soil that is excavated to a certain depth. OD consists of an aeration basin in