Effects of nonylphenol and nonylphenol ethoxylates on nitrification process

Growth of the population causes increasing of consumption. To supply the demands, industries try to find solution such as producing with lower production cost. Surface active agent, surfactant, are the one the agents that can be produced with lower cost. Especially, they are preferred in cleaning industry. Surfactants are divided by four groups: anionic, cathonic, nonionic and amphoteric (both anionic and cathionic). Nonionic surfacants are used in different types of industries such as cleaning, textile, paper and pulp, personal care etc. Best known nonionic surfactant is nonylphenol (NP). NP is commonly used in cleaning agents such as detergants. Nonylphenol is defined as a member of alkylphenol group in terms of chemical structure. It has alkyl chain and phenol structure. Alkyl chain is the hydrophobic part and the phenol structure is the hydrophilic part of the NP. NP cannot be biodegraded and disposed entirely after usage. Therefore, when they are discharged into the water body, they may be harmful for aquatic life and humans. Industries use NP components as nonylphenol polyethoxylate (NPnEO). NPnEO can be formed as NP2EO and NP1EO in aerobic and anaerobic environment. Its ethoxylate chain is getting smaller and it turns into NP, which is most hydrophobic type of nonylphenol components. When NP components get into wastewater treatment plant, NP is absorbed by the sludge. Chemical formula of the NP is C15H24O. Moleculer weight is 220 g/mole. Its melting point is -10ᵒC and boiling point is 304ᵒC. At standard conditions, NP is liquid with high viscocity and yellowish white color. Chemical structure of NP looks like estrogen hormone. Because of its characteristic structure, when it is taken up by the animals or people; body percieves NP as estrogen hormone. It may cause hormonal disease such as infertility and accumulation of toxicity while pregnancy. By considering side effects of NP components, goverments and agencies introduce some restrictions for usage and discharge of NP components. NP is in the endocrine disruptors list which is prepared by USEPA. REACH prepared by European Parliment and Council classify NP as dangerous chemical. European sludge directive limit the concentration of NP in the wastewater treatment plant sludge. NP should be below the 50 mg/kg in the sludge. Concentration of NP components in surface water can change according to countries and seasons. Surface water bodies in asian countries such as Korea, China, Thailand, Vietman has higher NP concentration compared to European countries. Generally, NP concentration is higher in summer months because of the increasing of usage shampoo and detergents. NP components concentrations are very low in ground water. NP may not only harmful for environment, but also inhibitor for wastewater treatment plants. There are different techniques using treatment of NP component, such as ozonation, coagulation, granular activated carbon, aerobic and anaerobic treatment etc. In these study, active sludge system is applied to obtain effect of nonylphenol compunds on carbon removal and nitrification process. 2 reactor is prepared for activated sludge system with 6 L volume each. Each reactor is operated as sequencing batch reactor. Sludge age is set as 10 days and temperature is kept at 24±1ᵒC. First, for acclimation activated sludge is fed with peptone solution which is readily biodegradable. Peptone solution is 400 mg COD/L. Macro and micro nutrients are added into the reactors also. After 4 months, acclimation is done and steady state conditions is recheaved. In this state, TSS concentration is 2000 mg/L and VSS concentration is 1245 mg/L. Effluent sCOD is measured as 57 mg/L. That means the removal efficiency of systen is 86%. After steady state condition, respirometric experiment is done. In the experiment, after reaching the stable endogenious respiration level; peptone is fed to the system and oxygen uptake rate is measured. During measurement, TSS, VSS, sCOD, pH, Nitrite-N and Nitrate-N samples are taken at spesific times from the experiment reactor. After the acclimation of activated sludge, NP compoent (as NP10EO) is added into the system with peptone feeding. NP10EO has 660 g/mole moleculer weight with (C2H4O)10C15H24O molecular formula. The COD concentration of peptone 400 mg/L and the COD concentration of NPEO is 400 mg/L. After adding NPEO, TSS concentration decreses for a while. At this period, respirometric experiments are done. As same as the fist experiment, after endogeneous decay is stable, peptone solution is added into the system with NPEO solution. While the oxygen uptake rate is measuring by the respirometer; TSS, VSS, pH, sCOD, Nitrite-N, Nitrate-N and NPEO samples are taken at spesific times. To determine the nitrification process, in some of the respirometric experiments nitrification inhibitor is added into the system. After 6 months, system is acclimated by peptone and NPEO. System is operated approximately 2.5 years and respirometric experiments are done. After stable condition is reached, some measurements are done with the samples taken from the reactors. At that time, TSS concentration is 2400 mg/L, VSS concentration is 1635 mg/L. Effluent soluble COD concentration is 162 mg/L which means the removal efficiency is 80%. After endogenious state, peptone and NPEO is added into the system and the oxygen uptake rate is measured by the respirometeric equipment. As same as previously experiments, during this respirometric experiment, TSS, VSS, pH, sCOD, Nitrite-N, Nitrate-N and NPEO samples are taken at spesific times. Last step of the study is aerobic stabilization process. System feeding is stopped and 2 reactors are combined. Total suspended solid concentration is measured as 8320 mg/L after combination. During 20 days, system is aerated and TSS, VSS, pH, sCOD, and NPEO samples are taken and measured each day. At the end of the stailization process, TSS removal efficiency is 36% and VSS removal efficiency is 54%. The data taken from the respirometric experiments are used for modelling. For each experiments (only peptone feeding and pepton/NPEO feeding) peptone solution has heterotrphic growth rate (𝜇̂𝐻) is 7.2 day-1 L and half saturation constant is is 20 mgCOD/L. Hydrolising rate of the nonylphenol ethoxylate is high (2.1 day-1). Yield for NPEO is 0.5 mg cellCOD/mg COD. This study aims that the obtain of effects of nonylphenol compunds on nitrification process in a activated sludge system. The increase of usage of nonylphenol, may cause some problems for environmental and people. Side effects of the nonylphenol is being researched and restrictions are applied for usage and discharge of NP compounds. However, the side effects of the nonylphenol compound on the wastewater treatment plant operations are not well known. With this study, the inhibition effect of the nonylphenol compound is not viewed.