Pollution profile and waste minimization study for a corn processing industry

Bu çalışmada Marmara Bölgesi’nde faaliyet gösteren büyük bir mısır işleme endüstrisi için kirlenme profili oluşturularak, çeşitli atık azaltım önerileri getirilmiştir. Bu amaçla söz konusu tesiste oluşan atıksu kaynak ve miktarları ile atıksu dışındaki atıkların tür, miktar ve özellikleri incelenmiştir. Tesiste üretim sürekli olup, ıslak öğütme ve rafineri olmak üzere iki temel proses mevcuttur. Tesisin üretim kademesindeki her bir işlem esnasında oluşan kirlilik konsantrasyonu belirlenerek kirlilik profili oluşturulmuştur. Endüstrinin biyolojik ve kimyasal kısımdan oluşan üç kademeli ileri atıksu arıtma tesisinin verimi ile deşarj suyunun kalitesi incelenerek ulusal ve uluslararası deşarj standartlarıyla kıyaslanmıştır. Kirlenme profilinin oluşturulmasında 2004-2005 dönemine ait bir yıllık kompozit numune bazlı analiz sonuçları dikkate alınmıştır. Kirlenme profili için KOİ yükü, deşarj suyunun değerlendirilmesinde ise KOİ, amonyak, nitrat, toplam fosfor ve askıda katı madde parametreleri incelenmiştir. Tesis için oluşturulan kirlenme profili incelendiğinde birim ürün başına oluşan atıksu miktarının rafineri prosesinde literatürle uyumlu olduğu; ıslak öğütme prosesinde ise literatür değerinin üstünde olduğu görülmüştür. Birim ürün başına KOİ yükleri incelendiğinde ise tesis değerlerinin literatür değerinin altında kaldığı görülmüştür. Atıksu oluşumu ve kirlilik açısından en önemli payı ıslak öğütme prosesinde yer alan evaporatör kondanse suyu oluşturmaktadır. İşletmenin arıtma tesisi performansına bakıldığında ise çıkış suyu değerlerinin ilgili ulusal ve uluslar arası yönetmelik limitlerini rahatlıkla sağladığı görülmektedir. Anahtar Kelimeler: Atık azaltımı, ileri atıksu arıtımı, kirlenme profili, mısır işleme endüstrisi.Products such as starch, gluten, glucose, dextrin, fructose etc. can be obtained from corn processing. Corn based glucose products are key ingredients in the growing international markets. As the intermediate products, the vegetable oil is bought by catering factories, protein and whole-wheat are bought by the farmers for animal feed, and fructose obtained from the starch is bought by food processing industries for sweetening and beverage. Effluent from corn milling industry is known as high strength wastewater due to its high protein and starch content. Wastewater from corn wet mill industries has high COD?s (chemical oxygen demand) mainly of soluble and biodegradable character, with an initial inert COD content of less than 15%. This character has promoted the application of biological processes as appropriate treatment technology. Anaerobic and/or aerobic biological treatment systems have been used to treat these types of effluents. In this paper, a pollution profile study for a corn processing industry located in Marmara Region as 21 ha was performed and some waste minimization approaches were proposed. For this purpose, the sources and the quantities of wastewater and other types of wastes generated in the industry were investigated. Around 264000 tons of corn are processed and 997000 tons of water are used annually in the investigated industry. The mean specific water usage can be calculated as  about 3.8 m3/t-corn including regeneration and washing waters. The studied industry has a three-stage advanced wastewater treatment plant (WWTP) including anaerobic expanded granular sludge bed reactor (EGSB), intermittently aerated single sludge activated sludge system for biological nitrogen (N) removal and chemical post treatment unit for phosphorus (P) removal. Simultaneous C and N removal is achieved by the aerobic treatment stage. Chemical P removal has been performed by using FeCl3 as the coagulant in the third stage. The final effluents from the WWTP are discharging to a nearby creek. The related corn processing plant has two main production steps including wet mill and starch slurry production. In the wet mill process, corn germ, fiber, gluten and starch slurry are produced from corn by steeping. The starch slurry is further processed to produce glucose, fructose and dextrin in the starch slurry derivatives units. Efficiency of the existing three stage advanced wastewater treatment plant and the quality of effluents from the WWTP were investigated and compared with national and international discharge standards. One year data set (2004-2005) was considered to generate the pollution profile. All analytical measurements have been carried out by APHA standard methods at the wastewater laboratory of the industry. Control analyses have also been performed by Environmental Engineering Department of Istanbul Technical University on monthly basis. COD parameter for the pollution profile and parameters including COD, ammonium, nitrate, total phosphorus, suspended solids and pH were considered for the evaluation of effluents from the WWTP. The identified three wastewater sources from the wet mill process and seven wastewater sources from refinery process were characterized and the pollution profile was generated. The pollution profile have shown that the amount of wastewater generated per ton of raw material in the refinery process is consistent with the related literature, however in wet milling process the corresponding value is above the literature figure. The COD loading values are also in agreement with the previous works. According to pollution profile, wastewater generation and pollutant loads as COD are mainly originated from evaporator vapor condensate. The efforts should be on the way to minimize the pollution loading and wastewater generation of this process. Some advices were given for this purpose in the study. For example, recycled cooling water from evaporator may be treated by mechanically instead chemical treatment to reduce energy and water consumptions in the plant. The quality of the final effluent meets the discharge limits of Aquatic Products and Water Pollution Control Regulations of Turkey and European Union (EU) Urban Wastewater Directive for Sensitive Regions. The whole WWTP has been operated very successfully and it is one of the best plants in this sector. The biosolids from the WWTP is planning to produce compost by mixing the residual corn wastes by applying windrow composting. Keywords: Advanced wastewater treatment, corn processing industry, pollution profile, waste minimization