Inhibition effect of heavy metals on the activated sludge

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1993Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 1993Kullanılmış sularda inhibitor adı verilen evsel ve özellikle endüstriyel kaynaklı maddeler bulunmaktadır. Ağır metaller ve bazı zehirli maddeler inhibitörlere örnek olarak gösterilebilir. Bu maddeler biyolojik gelişmeyi engelleyici etkilere sahiptirler ve antma tesislerinde verim azalması gibi sakıncalara yol açmaktadırlar. İnhibitörlerin kullanılmış sulardaki miktarı gelişen teknolojiye paralel olarak gün geçtikçe artmaktadır. Bu çalışmada da ağır metallerin biyolojik antma yöntemlerinden biri olan aktif çamur prosesine etkisi incelenmiştir. 1300 mg/1 KOİ içeren sentetik bir atıksuya 10 mg/1 kadmiyum ilavesiyle aktif çamura etkisi bir kemostat sistemde farklı çamur yaşlan için incelenmiştir. Sentetik atıksuyun organik madde kaynağı olarak proteoz - pepton kullanılmıştır. Aynca, kadmiyumun sistemdeki giderimi ve sistemde meydana gelen işletme problemleri ele alınmıştır. Çalışmada meydana gelen işletme problemleri ve süre kısıtı nedeniyle kinetik sabit tayini yapılamamıştır. Fakat kadmiyumlu sistemde peptonlu sisteme göre genel bir verim düşüklüğü saptanmıştır. Metal giderim verimi sonuçlanndan sistemde % 60 oranında metal giderilebileceği görülmüştür. Kadmiyum giderim verimi için bulunan bu değer literatürle uyum içerisindedir. Sistem işletme açısından incelendiğinde ise peptonlu sistem zaten olumsuz koşullara sahip olduğu için kadmiyumlu sistemde buna göre önemli bir fark gözlenmemiştir.The presence of inhibitors in wastewater is of concern, in terms of both the discharges of inhibitor into receiving waters which may be detrimental to the environment and reduced efficiency in biological wastewater treatment plants. Greater emphasis has been given on the efficient and effective treatment of wastewaters in recent years because of the passage of increasingly stringent effluent requirements, which has led to a revived interest in the effect of various toxic materials on biological treatment processes. As a result, research has been undertaken to increase the level of understanding of the effects of such inhibitors. Heavy metals are one of the most toxic group which strongly reduces the activity of microorganisms in activated sludge systems and also decreases the quality of receiving media. The aim of this study is to investigate the inhibition and its consequences of in the activated sludge by heavy metals. In this manner, the effects and removal of cadmium in activated sludge system have been searched by using experimental techniques. In biochemical reactions any effect which hinders the formation or reduces the rate of the reaction is called inhibition and the factors causing these effects are termed inhibitors. Most important factors for the biological activity are the concentrations of the food and energy sources existing at the environment. This concept is valid only when the environmental conditions are at normal levels and when no inhibitor exists. Existence of the inhibitors affect the biological growth. Inhibition of biochemical reactions is subject to the reduction of the activities of enzymes catalyzing the reactions or changes at the permeability of the cell wall. IX Generally two types of inhibition are considered; the first one is competitive inhibition where the inhibition degree depends on the substrate concentration. The second type is non-competitive inhibition. Heavy metals are considered as non-competitive inhibitors. In the literature, many methods developed for the evaluation of effects of inhibition upon the activated sludge. The methods mostly employed to measure the effect of heavy metals depend on the determination of activity, changes in biochemical or chemical oxygen demand, oxygen uptake rate, enzyme inhibition or nitrification rate. Due to the complexity of the inhibition mechanisms, measuring or evaluating the effects is difficult. The methods used for removal of heavy metals from wastewaters are mostly chemical or physical processes such as hydroxide or sulfide precipitation, ion exchange, membrane processes, etc. But these methods are feasible for industrial units. For domestic wastewaters which contain relatively low concentrations of heavy metals, the activated sludge system is widely used to remove heavy metal while treating the organic substances. Consequently it can be said that low metal concentrations have little effect on activated sludge systems. In some studies it is shown that low metal concentrations have a positive effect on the growth. Oh the other hand some studies indicate that metals have an inhibitory effect, however, they rarely cause the death of organisms unless extreme concentration are reached. The degree of the effect of heavy metals on the activated sludge depends on the ratio of the total metal concentration to the total suspended solids of the system. When this ratio increases, the removal efficiency of the system decreases. This decrease is because of the interactions between the cell components and the heavy metals resulting in the formation of metal-enzyme complexes. The literature survey showed that heavy metals are removed up to a certain extent in biological treatment. Metals can be removed in biological treatment at primary sedimentation or activated sludge stages. Every metal has a different removal efficiency in the system. It should also be considered that the metal accumulated in the waste sludge may cause some undesirable effects to the environment when land applications are practiced to dispose of the sludge. In order to avoid this problem some treatment techniques should be developed to remove the metals from waste sludge. There have been numerous studies in the literature on the subject of metal inhibition. Experimental studies are run to determine the effect of metal ions on activated sludge systems treating domestic wastewaters or synthetic wastewaters having similar characteristics as domestic wastewaters. However, the studies on the inhibition effect at high substrate concentrations are very limited. On the other hand, there is no study for cadmium inhibition at high substrate concentration systems. The presence of heavy metals may also cause operational problems in activated sludge plants. It is reported by various researchers that sludge bulking problems have been observed. It is also pointed out that turbidity problems may occur in relation to heavy metal inhibition. In this context, the purpose of this study is to investigate the effect of cadmium to the activated sludge treating high substrate concentration, to evaluate the metal treatment capability of activated sludge and operational problems caused by the metal. In the experimental planning stage, accordingly, proteose -peptone was selected as substrate and the feeding concentration of substrate was 1300 mg/1 COD. By considering the kinetic parameters of the system, residence times are chosen in the range of 0.5 to 1 day. Experiments were run in a series of chemostat reactors. The cadmium concentration for the evaluation of inhibition effect is determined as 10 mg/1. XI COD and suspended matter are measured to evaluate the system performance. Sludge volume index and total suspended solids concentration in treated phase are the parameters to control the operational efficiency of the system. Metal analysis are done to evaluate metal removal on the filtered phase and solid phase of the samples obtained from activated sludge aeration tank. The inert soluble COD of the synthetic wastewater is assessed according to the comparison method which was developed by Germirli, (1990). This method consisted of running two parallel batch reactors started with acclimated seed and with the same initial COD, one with the wastewater tested and the other with the glucose. When the test is continued for a period long enough to entirely deplete the degradable substrate, the difference between the COD level in the reactor operated and that of in glucose is assumed to be equal to SI0. Results and conclusions of the study are summarized as follows; -The kinetic constants for the activated sludge systems operated with peptone and peptone + cadmium could not be accurately determined because of the variations in the system efficiencies which prevented the attaintment of steady- state during the experimental phase of the study. The residual COD of the peptone system and viability of the suspended solids are measured and calculated to assess if these parameters has a marked effect on the determination of kinetic parameters. The results show that the viability of the system is very high being over 90 % and the residual COD is around 60 mg/1. However, a comparison of the average efficiencies of the two systems indicated a reduction of substrate removal efficiency in the system with cadmium. The degree of the loss of efficiency is similar to those given in the literature. - The results of the experiments concerning the metal removal efficiency showed that the system has a capability of 60 % cadmium removal. This value is slightly lower than the ratio reported in the literature. -When the systems are evaluated in terms of operation, it is not possible to compare the effects of cadmium on the system, because the peptone system itself showed poor operational stability as measured by SV1 and suspendedYüksek LisansM.Sc