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During coke production, large volume of effluent is generated, which has a very complex chemical composition and contains several toxic and carcinogenic substances, mainly aromatic compounds, cyanide, thiocyanate and ammonium. The composition of these high-strength effluents is very diverse and depends on the quality of coals used and the operating and technological parameters of coke ovens. In general, after initial physicochemical treatment, biological purification steps are applied in activated sludge bioreactors. This review summarizes the current knowledge on the anaerobic and aerobic transformation processes and describes key microorganisms, such as phenol- and thiocyanate-degrading, floc-forming, nitrifying and denitrifying bacteria, which contribute to the removal of pollutants from coke plant effluents. Providing the theoretical basis for technical issues (in this case the microbiology of coke plant effluent treatment) aids the optimization of existing technologies and the design of new management techniques., (© 2020. The Author(s).)

Pyridine is a typical nitrogen heterocyclic and recalcitrant organic compound in coking wastewater. The pyridine-degrading bacterial strain KDPy1 was isolated from aerobic sludge in a coking wastewater treatment plant. The homology analysis based on 16S rDNA sequences suggested that KDPy1 belongs to Rhodococcus sp. The optimum temperature and pH for pyridine degradation by KDPy1 were 37°C and 7-8, respectively. The strain KDPy1 degraded 1442 mg/L of pyridine nearly 99.6% after 48 h, and the high concentration of 1442 mg/L pyridine did not show an inhibitory effect on its degradation. The degradation kinetics of pyridine were fitted with the Monod model. Furthermore, KDPy1 was capable of degrading pyridine efficiently in the synthetic wastewater containing quinoline and phenol. KDPy1 could degrade pyridine and reduce the total organic carbon in the real coking wastewater. These results showed that KDPy1 had a potential for improving the removal of pyridine from coking wastewater.

Quinoline is a refractory organic compound in the treatment of coking wastewater. The isolation of high efficiency quinoline-degrading bacteria from activated sludge and the evaluation of their degradation characteristics in the presence of phenol or in the actual coking wastewater are important for the improvement of effluent quality. The novel bacterial strain Pseudomonas aeruginosa KDQ4 was isolated from a quinoline enrichment culture obtained from the activated sludge of a coking wastewater treatment plant. The optimum temperature and initial pH for quinoline degradation were 33-38°C and 8-9, respectively. KDQ4 completely degraded 400 mg/L of quinoline within 24 h and 800 mg/L of phenol within 30 h. In the dual-substrate system, the removal efficiencies of quinoline and phenol at the same initial concentration (200 mg/L) by KDQ4 were 89% and 100% within 24 h, respectively, indicating that KDQ4 could simultaneously and quickly degrade quinoline and phenol in a coexistence system. Moreover, KDQ4 was able to adapt to actual coking wastewater containing high quinoline and phenol concentrations and rapidly remove them. KDQ4 also exhibited heterotrophic nitrification and aerobic denitrification potential under aerobic conditions. These results suggested a potential bioaugmentation role for KDQ4 in the removal of nitrogen-heterocyclic compounds and phenolics from coking wastewater.

The bioaugmentation strains for phenol, pyridine, quinoline, carbazole, and naphthalene degradation were employed to treat coking wastewater in a membrane bioreactor (MBR). The results showed that the bioaugmented MBR was much better in pollutant removal than that of the control MBR with conventional activated sludge. Compared to the control MBR, the bioaugmented MBR displayed an additional 3.2 mg/L of phenol, pyridine, quinoline, naphthalene and carbazole in total by the addition of the degrading strains. Also, about 10 % of the chemical oxygen demand in the effluent was further removed by the bioaugmentation. The pyrosequencing analysis of the sludge in the MBRs revealed that the microbial community shifted in response to the addition of the degrading strains. The diversity of the microbial community increased during the bioaugmentation, and some bacterial taxa favorable to the removal of toxic and refractory pollutants appeared in the bioaugmented MBR. The results indicated that the use of high-efficiency bacteria was a feasible method for industrial coking wastewater treatment.

A taxonomic study was carried out on strain GCS-AN-3(T), which was isolated from a phenol-degrading consortium enriched from coking wastewater activated sludge of Beijing Shougang Company Limited during the screening of phenol-degrading bacteria. Cells of strain GCS-AN-3(T) were Gram-stain-negative, short rods, and oxidase-/catalase-positive. Growth was observed at salinities from 0 to 2.5 % and at temperatures from 10 to 37 °C. 16S rRNA gene sequence analysis showed that strain GCS-AN-3(T) was most closely related to Ottowia pentelensis DSM 21699(T) (96.2 %). The principal fatty acids were summed feature 3 (C16 : 1ω7c/C16 : 1ω6c), C16 : 0, summed feature 8 (C18 : 1ω7c/C18 : 1ω6c) and cyclo C17 : 0. The major respiratory quinone was Q-8. The polar lipids comprised phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine and an unknown phospholipid. The G+C content of the genomic DNA was 67.6 mol%. Thiosulfate could be utilized as co-substrate for aerobic growth and was oxidized to sulfate. On the basis of phenotypic, chemotaxonomic and molecular data, strain GCS-AN-3(T) is considered to represent a novel species of the genus Ottowia, for which the name Ottowia beijingensis sp. nov. is proposed (type strain GCS-AN-3(T) = LMG 27179(T) = CGMCC 1.12324(T) = MCCC 1A01410(T)). An emended description of the genus Ottowia is also proposed.

A metagenomic approach was taken to retrieve catabolic operons for aromatic compounds from activated sludge used to treat coke plant wastewater. Metagenomic DNA extracted from the sludge was cloned into fosmids and the resulting Escherichia coli library was screened for extradiol dioxygenases (EDOs) using catechol as a substrate, yielding 91 EDO-positive clones. Based on their substrate specificity for various catecholic compounds, 38 clones were subjected to sequence analysis. Each insert contained at least one EDO gene, and a total of 43 EDO genes were identified. More than half of these belonged to new EDO subfamilies: I.1.C (2 clones), I.2.G (20 clones), I.3.M (2 clones) and I.3.N (1 clone). The fact that novel I.2.G family genes were over-represented in these clones suggested that these genes play a specific role in environmental aromatic degradation. The I.2.G clones were further classified into six groups based on single-nucleotide polymorphisms (SNPs). Based on the combination of the SNPs, the evolutionary lineage of the genes was reconstructed; further, taking the activities of the clones into account, potential adaptive mutations were identified. The metagenomic approach was thus used to retrieve novel EDO genes as well as to gain insights into the gene evolution of EDOs.

A laboratory-scale anaerobic sequencing batch reactor (ASBR) was used to pretreat coking wastewater. Inoculated anaerobic granular biomass was acclimated for 225 d to the coking wastewater, and then the biochemical methane potential (BMP) of the coking wastewater in the acclimated granular biomass was measured. At the same time, some fundamental technological factors, such as the filling time and the reacting time ratio (t(f)/t(r)), the mixing intensity and the intermittent mixing mode, that affect anaerobic pretreatment of coking wastewater with ASBR, were evaluated through orthogonal tests. The COD removal efficiency reached 38%-50% in the stable operation period with the organic loading rate of 0.37-0.54 kg COD/(m(3).d) at the optimum conditions of t(f)/t(r), the mixing intensity and the intermittent mixing mode. In addition, the biodegradability of coking wastewater distinctly increased after the pretreatment using ASBR. At the end of the experiment, the microorganism forms on the granulated sludge in the ASBR were observed using SEM (scanning electron microscope) and fluoroscope. The results showed that the dominant microorganism on the granular sludge was Methanosaeta instead of Methanosarcina dominated on the inoculated sludge.

Parallel hybrid modeling methods are applied to a full-scale cokes wastewater treatment plant. Within the hybrid model structure, a mechanistic model specifies the basic dynamics of the relevant process and a non-parametric model compensates for the inaccuracy of the mechanistic model. First, a simplified mechanistic model is developed based on Activated Sludge Model No. 1 and the specific process knowledge of the cokes wastewater treatment process. Then, the mechanistic model is combined with five different non-parametric models--feedforward back-propagation neural network, radial basis function network, linear partial least squares (PLS), quadratic PLS and neural network PLS (NNPLS)--in parallel configuration. These models are identified with the same data obtained from the plant operation to predict dynamic behavior of the process. The performance of each parallel hybrid model is compared based on their ease of model building, prediction accuracy and interpretability. For this application, the parallel hybrid model with NNPLS as non-parametric model gives better performance than other parallel hybrid models. In addition, the NNPLS model is used to analyze the behavior of the operation data in the reduced space and allows for fault detection and isolation.

New phenol degrading bacteria with high biodegradation activity and high tolerance were isolated as Burkholderia cepacia PW3 and Pseudomonas aeruginosa AT2. Both isolates could grow aerobically on phenol as a sole carbon source even at 3 g/l. The whole-cell kinetic properties for phenol degradation by strains PW3 and AT2 showed a Vmax of 0.321 and 0.253 mg/l/min/(mg protein), respectively. The metabolic pathways for phenol biodegradation in both strains were assigned to the meta-cleavage activity of catechol 2,3-dioxygenase.