Süt endüstrisi atıksu arıtma tesisinin enerji verimliliğinin iyileştirilmesi
Energy-efficient upgrading of a large dairy industry waste water treatment plant
Yazar: EBUBEKİR AKKOYUN
Danışman: DOÇ. DR. MAHMUT ALTINBAŞ
İstanbul Teknik Üniversitesi / Enerji Enstitüsü / Enerji Bilim ve Teknoloji Ana Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Enerji = Energy

Özet:
Bu çalışmada bir süt tesisinin atıksu arıtma sistemi detaylı olarak incelenmiştir. İncelenen tesis geleneksel aerobik arıtma sisteminden anaerobik arıtma sistemine iyileştirmeler yapılarak geliştirilmiştir. İyileştirmeler sonrası enerji üreten bir tesis haline gelmiştir. Çalışmada özellikle atıksu arıtma tesisi içerisindeki üniteler incelenmiş ve tesisin işletme esanasında karşılaşılan problemleri analiz edilerek metodolojik yöntemlerle bulunması amaçlanmıştır. Tesisin akış şeması çıkarılarak tesis seçim kriterleri incelenmiş ve incelemeler sonucu anaerobik reaktördeki tasarım kriterleri ile deney sonuçları karşılaştırılmıştır. Süreç olarak iyileştirmelerden biri olan anaerobik kontak reaktörü sayesinde atıksuyun sistem çıkışında KOİ giderimi yasal sınırların altında kaldığı gözlenlenmiştir. Sistemdeki proses akışına göre reaktörler ve önemli görülen yerler üzerinden numuneler alınmış, numuneler laboratuvar ortamında analiz edilmiştir. İncelemeler sonucunda tesiste iyileştirme öncesinde kullanılan geleneksel aktif çamur tesisine ilave yapılan anaerobik temas reaktörü kendi giriş ve çıkış atıksu KOİ giderim etkinliği 328 günlük izleme sonucunda saptanmaya çalışılmıştır. Detaylı laboratuvar analizleri sonucu reaktör giriş çıkış arasındaki atıksuyun KOİ giderim oranı % 84 olarak bulunmuştur. Atıksu KOİ konsantrasyonu zamanın % 85'inde 650 mg/L'nin altında olduğu tespit edilmiştir. Yapılan deneyler sonucunda anaerobik temas reaktöründe biyokütleyi temsilen ölçülen AKM ve UAKM kademeli olarak 6000 mg/L 'ye yükselmiştir. Bu değerin yükselme sebepleri irdelenmiş bununla birlikte yapılan analizler sırasında biyokütleyi anaerobik reaktörde tutmanın zor olduğu görülmüştür. Buna ilave olarak ikinci aşama olan aerobik biyolojik konvansiyonel (aktif çamur) sisteminin atık KOİ konsantrasyonu, zamanın %85'inde 47 mg/L 'in altında olduğu tespit edilmiştir. Anaerobik çamur çürütücüsünden çıkan sıvı doğrudan gübre olarak kullanılması mümkün olup ayrıca tesiste yer alan dekantör ile katı sıvı ayrımının yapılması da mümkündür. Santrifüj dekantör ile ayrıştırılan çamurun sıvı kısmı atık aktif çamur sistemine devirdaim edilerek atıksu olarak işlem görmektedir. Anaerobik reaktörden elde edilen biyogaz içten yanmalı gaz motorları ile yakıldıktan sonra ısı ve elektrik enerjisi elde edilmektedir. Bu kapsamda gaz motoru kısmındaki verim artışı incelenmiş ve 26400 kWh/gün elektrik enerjisi üretmek mümkün olduğu tespit edilmiştir. Tesisin sadece aerobik sistem var iken işletme maliyeti ile yeni anaerobik sistem kurulduktan sonraki işletme maliyetleri ekonomik açıdan değerlendirilmiş ve yatırımın geri dönüş süresi hesaplanmıştır.

Abstract:
In this study, wastewater treatment system of a large dairy plant was investigated. The investigated plant is an upgraded facility with improvements from the traditional aerobic treatment system to the anaerobic treatment system. After the improvements, it has become an energy producing facility. 
In WWTP, firstly, investigations were make and the process was tried to be understood. Appropriate sample points for wastewater analysis were identified with the process inspection. The existing sampling points of the facility are investigated in the literature. By examining the studies on this subject previously, it has been observed that the sampling points are correct. While examining the studies in the literature, the methodology of the measurement of dairy industry wastewaters was investigated in the early stages of the study. During the research, it was observed that COD removal rate was the main parameter among the parameters that should be measured.
Thanks to the anaerobic contact reactor, which is one of the improvements in process, COD removal at the system outlet of wastewater is below the legal limits. In this study, the sections in the wastewater treatment plant were examined and the problem was determined by the methodological methods.
Characterization of WWTP wastes was determined, it was compared with old experiences. The values of COD were checked with laboratory analyses.  COD values were observed in accordance with the values in the literature. The facility processes 850 m3 of milk per day and produces 5000 m3/day of waste water for milk and dairy products, yoghurt, cheese, milk sweet products as well as fruit juice, ketchup, mayonnaise and powder products. According to the revision of the wastewater treatment plant, a flow rate of 6920 m3/day was chosen. Waste Flow 6920 m3/day; pH 9-11; COD 3500 mg/L; BOD is 1500-2000 mg/L; AKM 800 mg/L; oil and grease 400 mg/L; TKN is 100-200 mg/L and TP is 1-3 mg/L. The plant obtained from the factory for the purification processes and energy efficiency of the plant are combined here and laboratory measurements.
Dairy industry effluents can be treated by physico-chemical and biological methods. Due to the high cost and low COD removal efficiency, physico-chemical methods are not widely preferred, except for the separation of fatty and suspended solids. The treatment of dairy wastewater with aerobic processes is less efficient and has significant problems, such as excessive biomass formation, and foam generation in addition to its high cost of aeration. Anaerobic processes are efficient than the aerobic processes, decreasing to organic content of different wastewaters without oxygen. Therefore, biomethane recovery is one of the main alternatives for anaerobic treatment of dairy effluents having low energy cost, low sludge formation, as well as low nutrient requirements.
Anaerobic contact reactors have relatively higher biomass concentration, greater efficiency, and smaller reactor size which makes them cost-efficient and sustainable. Sludge recycling allows longer contact between biomass and raw wastewater.
Dairy industry waste characterization was explained with old experiments. Requirement of anaerobic treatment in dairy industry was tried to explain.  WWTP detailed flow chart was showed and section of WWTP was explained, new sections working criterias was reviewed with mathematical analysis. Equipments capacities examined with design capacity. Anaerobic contact reactor, DAF unit, aerobic reactor operating values founded to expected values with design capacities. 
According to the process flow in the system, samples were taken from tanks and important places and samples were examined in laboratory. As a result of the investigations, it has been tried to determine the efficiency of COD removal in the influent and effluent wastewater of the anaerobic contact reactor which is added to the traditional activated sludge plant used before the improvement in the plant. 
During the plant examination, which parts of the wastewater came from the dairy plant were examined. The most important factor observed in the investigations is that hygiene-related washings in dairy products are the most important key performance indicators affecting the amount of wastewater. Washing water coming from the sections of the facility, remnants of dairy products in the pipes feeding the product lines, lost products from the start of production in the spaces constitute the significant amount of wastewater coming to WWTP. The COD levels in the dairy industry varied from 900 to 9000 mg / L. Other important parameters in milk industry characterization are BOD5, TKN and SS.
In order to determine the treatment performance and energy efficiency of the facility, the data obtained from the factory, and the detailed laboratory measurements were combined. In the detailed wastewater characterization, composite samples were taken at a 2-h interval for 24-h and the samples were stored at 4 oC prior to analysis. 
The performance analysis of the WWTP was carried out with COD, COD load, volumetric loading rate, organic loading rate, COD removal, TKN, NH4-N, TP, PO4-P, SS, VSS, oil and grease, sulphate, free chlorine, pH, conductivity, and temperature parameters using regular statistical analysis tools.
After detailed laboratory analysis, waste COD removal rate between reactor influent and effluent was found to be 84%. Because of 328 days experiments for waste COD removal, the COD concentration was found to be below 650 mg/L at 85% of the time. 
As a result of the experiments, SS and VSS gradually increased to 6000 mg/L in anaerobic contact reactor. Reasons for the increase of this value were examined, however, it was found difficult to keep the biomass in anaerobic reactor during the analyzes. Sludge leakage rootcause in the anaerobic reactor has been examined and the necessary studies are written in the results section. In addition to this, the second stage of the system, the aerobic biological conventional system (activated sludge), waste COD concentration, 85% of time was found to be less than 47 mg/L. The removal rate of the new anaerobic sludge digesters was analyzed methodologically, while it was observed that the solids used as direct manure were recycled to the activated sludge system. The flow chart of the plant were examined and as a result of the investigations, the design criteria of the anaerobic reactor and the experimental results were compared. Improvements to eliminate sludge leakage in anaerobic contact reactor were determined. Improvements were made experimentaly and the possible values were examined. 
Biogas producing of biomass in the anaerobic contact reactor was calculated. The values were compared with the analysis results. The biomass capacity of %85 was treated to biogas. The biogas which was storage in the membrane tank, Membrane stogare tank through to gas engine with the pipeline. Storage capacity is 1000 m3 and Storage tank can supply full capacity gas engine for 4 hours. It was showed enough for the sustainibilty of the operating to energy producing.
According to the results of detailed investigations based on the archive data available in the WWTP accompanied by a six-month observation period, it was concluded to generate 26400 kWh/day electrical energy with this system.  In the pre-upgraded system, high proportion of chemicals (caustic, flocculant & acid) was used to reduce the COD entering the aerobic treatment, since anaerobic treatment was missing. In the case of anaerobic treatment, DAF would continue to work (as a normal DAF- not as a chemical DAF), so that only floating oils that were harmful to anaerobic treatment would be retained. COD removal would not be appied in this unit, which would save 200,000 €/year of chemical costs.
Moreover, there was a high amount of chemical sludge formation during the use of DAF. This sludge was disposed of as a hazardous waste and 10950 tons of oily chemical sludge was paid 50 € ton/year which would save up to more 547500 €/year. After the anaerobic treatment was established, the COD entering the aeration was reduced to a great extent, and the number of ventilation ponds was reduced to 1, and the process of conventional activated sludge was started. Since the COD load decreased, 150 kW was sufficient instead of the 500 kW in previous conditions. Therefore, an annual electricity cost savings of € 252000 has also emerged.
 While there was only the aerobic system prior to anaerobic treatment, the biological sludge formed would be greatly reduced after anaerobic treatment and would be reduced more by digestion in the solid waste digester. In the previous situation, there was an estimated cost of 182500 €/year which decreased to 92722 €/year after upgrading.
After the upgrading of the system, 50% reduction in the initial aeration tank volume, and 70% reduction in the aerating power had been achieved, alongside a 50% decrease in sludge disposal costs. The improvement totaling an investment cost of 3 million € has been refunded in less than 2 years with the revenue of the generated biomethane energy, and other precautionary savings. The results demonstrated that anaerobic treatment for dairy effluent can indeed be considered as a very efficient and even income generating source.
Detailed economic analysis was examined end of the study. The investment costs and operating cost detailed determined with WWTP archive values. This analysis return on investment was given with detailed table. Return on investment value less than 2 years. It was examined to 1,65 years. The results demonstrated that anaerobic treatment for dairy effluent can indeed be considered as a very efficient and even income generating source.