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This study quantitatively evaluated the effects of pyrethroid pesticides on the testis of male rats. An extensive literature search for relevant studies was conducted on PubMed, Web of Science, Excerpta Medica Database, the Chinese National Knowledge Infrastructure, and Chinese Biomedical Literature Database. Pooled standard mean difference with corresponding 95% confidence interval was calculated via the random-effects model. I 2 was used to evaluate heterogeneity among studies. A total of 19 studies were included for analysis in our study. Results indicated that the sperm count of rats exposed to fenvalerate was lower than that of rats in control groups. The sperm count, sperm motility, and testosterone level of rats exposed to cypermethrin and deltamethrin were lower than those of rats in control groups. Moreover, the sperm morphology of rats exposed to these pyrethroid pesticides was abnormal compared with that of rats in control groups. The present meta-analysis indicates that pyrethroid pesticides decrease rat sperm count, sperm motility, and testosterone level and cause abnormal rat sperm morphology. Therefore, pyrethroid pesticides can damage the testis of male rats.

Activated sludge treated by ultrasound was tested as a source of exogenous electron donor to accelerate quinoline mono-oxygenation, which requires an intracellular electron donor (2H). The quinoline-removal rate was proportional to the amount of treated or untreated sludge added in flask experiments, but the best biodegradation kinetics was obtained with a mixture of 25% untreated sludge plus 75% treated sludge. The treated sludge primarily provided exogenous electron donor, while the untreated sludge provided active biomass. A biofilm system also showed the same beneficial effect of treated sludge, and the soluble fraction of the treated sludge had the greatest impact. Using treated sludge instead of a purchased electron donor provides an economic advantage for accelerating the biodegradation of contaminants whose biodegradation is initiated by an oxygenation reaction, such as quinoline.

Fallen leaves of Platanus orientalis and Ginkgo biloba linn were separately immersed in water to obtain leachates that were used as exogenous electron donors for accelerating pyridine and quinoline biodegradations. Leachate addition accelerated the pyridine removal rate by up to 4.4% and 3.6% and the quinoline removal rate by 9.5% and 11%. The rates increased further after the leachates were illuminated by UV light: up to 8.5% for pyridine and 12% for quinoline. Succinate and oxalate were separately added into solutions of pyridine and quinoline (respectively) to gauge the acceleration impact of the leaf leachates. Equations describing the relationships between addition of leachate and pyridine or quinoline removal rates were established based on electron-equivalent balances and comparison to the acceleration effects from succinate and oxalate. From 22% to 98% of the COD leached from leaves was available as an electron donor, with the fraction being greater for pyridine and after UV illumination.

Para-nitrophenol (PNP) is often detected in industrial wastewater that is discharged into municipal wastewater treatment plants. Intermittent discharge of PNP into municipal treatment facilities puts their biological process at risk of inhibition, and the risk is especially great for nitrification. In this work, nitrifying biomass was acclimated to PNP. The acclimated biomass retained most of its ammonium-removal activity when it was exposed to PNP at up to 100 mg/L, while the normal (unacclimated) biomass had nearly complete inhibition. PNP was effectively biodegraded by the acclimated biomass, but the normal biomass had minimal PNP biodegradation. After PNP disappeared, the acclimated biomass recovered its ability for NH4+-N removals within one to two days, but the normal biomass did not fully recovery even after seven days. The acclimated biomass had superior ability to sustain nitrification due to its ability to biodegrade PNP and its selection of nitrifying bacteria more resistant to PNP. The PNP-acclimated community was enriched in genera that could have been active in the biodegradation of PNP, such as Chloroflexi. Although the abundance of well-known nitrifiers, Nitrosomonas and Nitrospira, decreased, Nitrosospira and other genera within the Proetobacteria phylum increased, presumably because they were more resistant to PNP.

Many municipal wastewater treatment plants in China receive industrial wastewater that contains inhibitory organic chemicals, such as chlorinated phenols. For the common aerobic biological treatment, nitrification is a key step, but nitrifying bacteria are notably sensitive to inhibition by chlorinated phenols. In this work, normal activated sludge (containing nitrifying biomass) was acclimated to 2,4,6-trichlorophenol (TCP). The acclimated biomass had more than 2-fold faster nitrification kinetics than normal biomass when exposed to TCP, and it also achieved effective TCP removal in parallel. When suddenly exposed to TCP after as much as two months without TCP input, the acclimated nitrifying biomass retained effective nitrification and TCP biodegradation: The nitrification rate and TCP removal rate were 0.325 mM/h and 0.049 mM/h for the acclimated biomass, compared to only 0.165 mM/h and 0.001 mM/h for normal biomass. Resistance to TCP inhibition also was retained for 5 generations of sub-culturing without TCP exposure. High-throughput sequencing confirmed that the acclimated biomass contained nitrifying bacteria and heterotrophic bacteria capable of degrading TCP, although the key genera changed during sub-culturing.

It is common that phenol and quinoline co-exist in the same industrial wastewater, such as coking wastewater. For both biodegradations, the initial steps are mono-oxygenation reactions, which require two co-substrates: molecular oxygen (O2) and an intercellular electron donor (2H). Competition for O2 and 2H was investigated using a vertical baffled bioreactor (VBBR) with a biofilm acclimated to phenol and quinoline biodegradation. Batch experiments documented mutual inhibition between phenol and quinoline, which competed for O2, 2H, or both during simultaneous biodegradation. Low DO was a limiting factor for phenol and quinoline biodegradations, as both rates slowed significantly for DO ≤ 3 mg/L, compared to DO ≥ 5 mg/L. A DO concentration of 0.5 mg/L led to 89% and 65% slower removal kinetics for phenol and quinoline, respectively. Although adding succinate as an exogenous electron donor was able to alleviate competition when the DO was 4 ∼ 5 mg/L, it had no benefit for a DO ≤ 3 mg/L. Thus, significant DO limitation could not be overcome by addition of more donor. The results imply that a strategy that involves adding or creating an exogenous electron donor may be effective only when DO is not significantly rate limiting for the initial oxygenation reactions.

Aerobic biomass (acclimated activated sludge) was treated by ultrasound and used to accelerate biodegradations of pyridine and p-nitrophenol (PNP), which begin with mono-oxygenation reactions that need an internal electron donor. Ultrasound treatment disrupted the biomass and produced more soluble and (especially) colloidal organic material. Compared with untreated biomass, pyridine- and PNP-biodegradation rates increased when treated biomass provided electron donor. Pyridine- and PNP-biodegradation rates increased by 10% and 20%, respectively, over the control experiments when supernatants from treated biomass were added into the medium. For accelerating pyridine- and PNP removal rates, adding supernatants of treated biomass was equivalent to adding succinate of 0.35 mmol/L and 0.21 mmol/L, respectively. The rates were increased by 63% for both substrates when the entire treated biomass was added. Colloidal solids in the treated biomass contained most of biodegradable electron donor able to stimulate initial monooxygenations of pyridine and PNP. Adding treated biomass together with untreated biomass gave a synergistic impact on enhancing pyridine and PNP biodegradation, because the treated biomass supplied extra donor, while the untreated biomass maintained a high level of active biomass.

It is common that biological wastewater-treatment processes are exposed to inputs of toxic compounds, such as phenolics. Due to their slow growth rate, nitrifying bacteria are most susceptible to inhibition that can lead to loss of nitrification capacity. Here, a microbial community containing nitrifying bacteria was acclimated to phenol, and it developed resistance to phenol inhibition and maintained nitrification activity. For the phenol-acclimated biomass, the NH4+-N removal rates were almost unaffected when it was suddenly exposed to phenol. Heterotrophic synthesis and nitrification rates contributed 76% and 24% of the total NH4+-N removal respectively during phenol removal, but the nitrification rate increased significantly once phenol was removed and mineralized. In contrast, the NH4+-N removal rates decreased sharply for normal (unacclimated) nitrifying biomass when it was exposed to phenol. The phenol-acclimated biomass retained its resistance to phenol inhibition for at least two months after acclimation, and addition of the phenol-acclimated biomass to the normal biomass conferred resistance to phenol inhibition. Community analysis of the phenol-acclimated biomass showed an increase in families known to contain strains able to biodegrade phenolics. Taken together, the results indicate that the main impact of phenol acclimation was enrichment of phenol-biodegrading bacteria, which allowed rapid removal and mineralization of phenol and, consequently, alleviation of phenol's inhibition of nitrification.

Aerobic biodegradation of nitrobenzene (NB) produces nitrophenol (NP), which has stronger toxicity than NB. Anaerobic biodegradation of NB produces aniline (AN), which has weaker toxicity, but is a dead-end product in anaerobic conditions. Accumulation of AN should be overcome by coupling anaerobic and aerobic transformations: NB is transformed to AN in an anaerobic zone of the bioreactor, and AN is then transformed in an aerobic zone. A vertical baffled bioreactor (VBBR) was employed for NB biodegradation with a controlled dissolved oxygen (DO) concentration. NB biodegradation was accelerated by simultaneous anaerobic and aerobic transformations, since AN was biotransformed by a mono-oxygenase reaction. Adding exogenous electron donor (acetate) enhanced NB removals when the DO concentration was ∼0.5 mg/L, because the donor accelerated mono-oxygenations of NB and AN. Coupling anaerobic and aerobic transformations can be a valuable strategy for biodegrading organic compounds that undergo aerobic and anaerobic biotransformations.