Performance analysis of four-stage rotating biological contactor in nitrification and COD removal from petroleum refinery wastewater
Graphical abstract
Introduction
Petroleum refineries generate large amounts of priority pollutants that after recovery of oil in American petroleum institute (API) separators and removal of oil in dissolved air flotation (DAF) units, and the activated sludge process (ASP) is typically the biological treatment of this wastewater. Due to some problems with the suspended growth process, it can be replaced by fixed-film biological reactors such as the rotating biological contactor [[1], [2], [3]]. According to the United States, Environmental Protection Agency (USEPA) and World Health Organization (WHO), petroleum refining wastewater (PRW) have to be sufficiently treated for quality to meet the established regulations and they limited ammonia concentration to 2.5 mg/l in drinking water [4,5].
PRW with high ammonia content is generally difficult to treat effectively by conventional physical and chemical methods. Therefore, there is a great need to improve the existing biological treatment processes [[6], [7], [8]]. One of the most important methods used for ammonia removal from industrial wastewater is the biological methods using nitrification and denitrification processes [9]. Nitrification is a two-step microbial process in which two groups of autotrophic nitrifying bacteria are involved. In the first step, there is the conversion of ammonium nitrogen to nitrite by Nitrosomonas-like bacteria (Eq. (1)) and subsequently, in the second step there is the conversion of nitrite to nitrate by Nitrobacteria-like bacteria (Eq. (2)) [10,11]:
The rotating biological contactor is attached growth fixed biofilm reactor based on biomass that develops on the surface of a series of circular discs mounted onto a horizontal shaft with approximately 35–45 % of the discs submerged in the wastewater. Also, the rotating disc surface alternately partially immersed in the wastewater and comes into contact between air-water allows the transfer of oxygen and adequate an active thin layer of microorganisms development [[12], [13], [14], [15], [16]]. RBCs are widely used in industrial and municipal wastewater treatments by exploiting the advantages of both fixed film and suspended growth systems. RBC offers operational simplicity, low costs of operation and maintenance, low energy requirement, high biomass concentration, little sloughing of biomass, short hydraulic retention time (HRT), resistance towards shock loadings, and capability for handling toxic pollutants [[17], [18], [19], [20], [21], [22]].
RBC represents a viable means for nitrification and denitrification processes since the dominant microorganisms on biofilm were very stable and also grew very well on the discs. Nitrifying bacteria in RBC were the major organisms responsible for decreasing the total Kjeldahl nitrogen (TKN) level in the industrial wastewater treatment [[23], [24], [25]]. Previous studies have reported on the successful application of RBCs to the treatment of wastewaters containing ammonia [[26], [27], [28], [29], [30], [31], [32], [33], [34]].
To overcome the current limitations of ASP and based on the above background, the main objective of this work was to evaluate the effectiveness of a four-stage RBC for the simultaneous removal of COD and ammonia of PRW under variable hydraulic loading rate (HLR). Also, the effect of temperature, influent ammonia concentration, flow rate, and discs rotational speed on removal efficiency of ammonia and COD were evaluated. Finally, design expert software was applied for design, mathematical modeling, and optimization.
Section snippets
Experimental set-up
A bench-scale four-stage RBC was fabricated with a thick iron sheet that was coated with fiberglass [35]. The schematic experimental setup is shown in Fig. 1. The total volume of RBC was 16 L and a working volume of 8 L. The dimensions of the RBC reactor were 52 cm length, 28 cm width, and 11 cm depth which consisted of four-stages. The parameters of the experimental setup of the RBC reactor are shown in Table 1. Each stage was separated by fixed baffle plates that comprised one hole drilled
Regression models and statistical analysis
Regression models and statistical testing in this paper, correlations between the responses and independent variables were obtained by the following second-order model with a least square method [45]:Where Y is the response, B0 is a constant coefficient, Bj, Bij, and Bjj are the coefficients for linear, quadratic, and interaction effects, respectively. Xi and Xj are the coded levels for the independent variables; k is the number of independent variables
Conclusions
In this investigation, the performance of a four-stage RBC for continuous treatment of real wastewaters was evaluated. The mineral salts medium was used to enrich nitrifying bacteria for the oxidation of ammonia in refinery wastewater. Also, In the first stage, the maximum ammonia and COD removals efficiency occurred at the lowest and medium HLR. The increase of HLR due to the reduction of HRT seemed to have a negative effect on ammonia removal. Likewise, a negative correlation was observed
CRediT authorship contribution statement
Vahab Ghalehkhondabi: Methodology, Software, Validation, Writing - review & editing. Alireza Fazlali: Conceptualization, Supervision, Funding acquisition. Behrooz Fallah: Formal analysis, Investigation, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
The authors gratefully acknowledge the support provided by Shazand Petroleum Refinery Company (Arak, Iran).
References (45)
- et al.
Treatment of hydrocarbon-rich wastewater using oil degrading bacteria and phototrophic microorganisms in rotating biological contactor: effect of N: P ratio
J. Hazard. Mater.
(2008) - et al.
Treatment of aqueous effluents containing non-aqueous phase liquids in rotating biological contactor with algal bacterial biofilm
Chem. Eng. J.
(2012) - et al.
Benzene control from waste gas streams with a sponge-medium based rotating biological contactor
Int. Biodeter. Biodegr.
(2016) - et al.
Biological oxidation of gaseous VOCs–rotating biological contactor a promising and eco-friendly technique
J. Environ. Chem. Eng.
(2014) - et al.
BTEX biodegradation by bacteria from effluents of petroleum refinery
Sci. Total Environ.
(2010) - et al.
Enhanced biological denitrification in the cyclic rotating bed reactor with catechol as carbon source
Bioresour. Technol.
(2015) - et al.
Bioaugmentation for treating transient 4-fluorocinnamic acid shock loads in a rotating biological contactor
Bioresour. Technol.
(2013) - et al.
Simultaneous removal of carbon and nitrogen from municipal-type synthetic wastewater using net-like rotating biological contactor (NRBC)
Process Biochem.
(2006) - et al.
Removal of hydrocarbons in a rotating biological contactor with biodrum
Process Biochem.
(2005) - et al.
Model for oxygen transfer in rotating biological contactor
Water Res.
(2004)