Application of energy spilling mechanism by para-nitrophenol in biological excess sludge reduction in batch-activated sludge reactor

Takdastan and Eslami International Journal of Energy and Environmental Engineering 2013, 4:26 http://www.journal-ijeee.com/content/4/1/26 ORIGINAL RESEARCH Open Access Application of energy spilling mechanism by para-nitrophenol in biological excess sludge reduction in batch-activated sludge reactor Afshin Takdastan1* and Azadeh Eslami2 Abstract Reduction of biomass production coefficient is an ideal solution for the reduction of excess sludge especially in industrial wastewater treatment plants. Studies were carried out in two sequencing batch reactors, which were controlled online. After presenting a stable situation in reactors, during 24 months of the study, sampling and examining of chemical oxygen demand (COD), biochemical oxygen demand, pH, sludge volume index (SVI), specific oxygen uptake rate (SOUR), remaining pNP, and biomass yield (Y) were implemented. Results have shown that among different retention times (5, 10, 15, 25 days), maximum COD removal efficiency (95%) was achieved in 10 days, without bulking and foaming problems. In 10 days of sludge retention time, average Y and kinetic coefficient (Kd) were calculated: 0.58 mg biomass/mg COD and 0.058 1/day, respectively, and correlation coefficient (R2) was 0.98. Different concentration of pNP were used due to energy spilling effect in the reactor and the results show that injection of 100 mg/L pNP to the reactor can reduce synthetic coefficient Y from 0.58 to 0.27 mg biomass/mg COD without pNP injection, so that the excess sludge was reduced by 0.56%. Although, an increase of 193 mg/L soluble COD in the effluent was observed. On the other hand, in this concentration of pNP, SOUR rate reached 31 mg O2/h/g volatile suspended solids, and SVI rate reached less than 48 mL/g. In the concentration of 150 mg/L pNP, no sludge was produced, but COD rate of the effluent increased to 480 mg/L. Otherwise, pNP rate is an environmental limitation in effluent and sludge disposal. Keywords: Sequencing batch reactor; Biological sludge; Biomass yield; COD; Para-nitrophenol Background Removal of organic materials by biological oxidation is a core technology in wastewater treatment process. New cells (sludge), carbon dioxide, soluble microbial products, and water are the end products for this process. The activated sludge process is widely used for municipal and industrial wastewater treatment and generates a large quantity of excess sludge daily. So far, the ultimate disposal of excess sludge has been and continues to be one of the most expensive problems faced by wastewater utilities, e.g., the treatment of the excess sludge may account for up to 65% of the total plant operation cost. So in recent years, * Correspondence: 1 Department of Environmental Health and Environmental Technology Research Centre, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran Full list of author information is available at the end of the article increased attention has been given to the minimization of waste sludge in wastewater treatment process [1-6]. Reduction of biomass production in wastewater treatment was discussed when costs and difficulties of treatment and disposal of the sludge were considered. On the other hand, new rules and severe standards of reuse and disposal of the sludge about different organic and inorganic pollutants and pathogens forced wastewater treatment experts to invent aerated biological treatment methods which produce less sludge amount. In other words, if the problem of excess sludge production is solved, most of the problems would also be solved considerably in the treatment and disposal of the biomass [7,8]. Due to severe problems and heavy costs of operations of sludge treatment, mechanisms of biomass reduction were considered in the recent years. A collection of effective determinations in this field are: © 2013 Takdastan and Eslami; lincensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Takdastan and Eslami International Journal of Energy and Environmental Engineering 2013, 4:26 http://www.journal-ijeee.com/content/4/1/26 – Self-destructive process [9-12] – Uncoupled metabolism using OSA process [5,12-18] – Increasing soluble oxygen of aeration pond [19] – Oxidation of a part of sludge by chlorine or ozone [2,5,7,8,18,20-23] – Increasing temperature in returned sludge to the reactor [6,24-26] – Energy spilling by compounds resistant to degradation and toxicant [3-5,17,27-30] – pH changes [11,24] – Using electrical pulse in returned sludge [31] – Using ultrasonic waves in returned sludge [32] – Using bacteriophages such as protozoa and metazoan [33,34] For most of the aerobic bacteria, adenosine-5′-triphosphate (ATP) is generated by oxidative phosphorylation, in which process electrons are transported through the electron transport system from a source of electrons at elevated energy levels (substrate) to a final electron acceptor (oxygen). The chemiosmotic theory shows that the oxidative phosphorylation is driven by proton gradient built up across cell membrane [11]. However, the tight coupling of respiration and phosphorylation can be disturbed by molecules known as metabolic uncouplers. In the presence of metabolic uncouplers, the energy generated from the oxidation of organic substrate would be lost as heat rather than being captured in ATP. As a result, the growth efficiency is much lowered in uncoupler-containing microbial culture. Metabolic uncouplers include a diverse group of molecule-structures, but they are all lipophilic weak acids [5,29,35,36] many of which have been used to reduce excess sludge production from the activated sludge processes, such as nitrophenol, chlorophenol, 3;3′,4′,5tetrachlorosalicylanilide (TCS), 2,4,5-trichlorophenol (TCP), carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone, cresol, aminophenol, and so on [3,4,20,27-29,37,38]. In 1998, Mayhew and colleagues found that injecting 35 mg/L of 2,4 dinitrophenol to the activated sludge reactor in 20°C, 0.3 mg mixed-liquor suspended solids (MLSS)/g chemical oxygen demand (COD) in pH = 7, and 2.5 g/L MLSS, sludge retention time (SRT) = 15 Figure 1 Sequencing batch reactor (SBR) pilot plant. Page 2 of 7 days and hydraulic retention time (HRT) = 5.5 h can reduce biological excess sludge, but the only problem is a 3.7% COD increase in the effluent [38]. In 1998, Low et al., found that continuous injection of 100 mg/L paranitrophenol (pNP) to a culture media containing pseudomonas at 30°C and pH = 6.2 to 7 can reduce biological excess sludge from 62% to 70% [28]. In 1999, Strand and colleagues found that a 2 to 2.5 mg/L increase of TCP to the activated sludge continuously cultivated at 20°C and pH = 7, MLSS = 2.5 g/L, SRT = 5 days, HRT = 3.5 h can reduce biological excess sludge a (...truncated)