Integrated nutrient recycling: Ammonia recovery from thermophilic composting of shrimp aquaculture sludge via self-heated bench-scale reactor and mango plant growth enhancement by the compost.

Due to the rapid growth of the aquaculture industry, large amounts of organic waste are released into nature and polluted the environment. Traditional organic waste treatment such as composting is a time-consuming process that retains the ammonia (NH3) in the compost, and the compost produced has little economic value as organic fertilizer. Illegal direct discharge into the environment is therefore widespread. This study investigates the recovery of NH3 through thermophilic composting of shrimp aquaculture sludge (SAS) and its application as a soil conditioner for the growth of mango plants. A maximum composting temperature of 57.10 °C was achieved through self-heating in a 200 L bench-scale reactor, resulting in NH3 recovery of 224.04 mol/ton-ds after 14 days. The addition of calcium hydroxide and increased aeration have been shown to increase NH3 volatilization. The recovered NH3 up to 3 kg-N can be used as a source of clean nitrogen for high-value microalgae cultivation, with a theoretical yield of up to 34.85 kg-algae of microalgae biomass from 1 ton-ds of SAS composting. Despite the high salinity, SAS compost improved mango plant growth and disease resistance. These results highlight the potential of SAS compost as a sustainable source of clean nitrogen for microalgae cultivation and soil conditioner, contributing to a waste-free circular economy through nutrient recycling and sustainable agriculture.

Evaluation of Fecundity, Fertilization, Hatching, and Gonadosomatic Index of Exotic Clarias gariepinus (Burchell, 1822) and Native Clarias macromystax (Gunther, 1864) under Semi-Arid Conditions of Nigeria.

The study evaluates the hybridizations between two African catfish, C. gariepinus and C. macromystax, using artificial reproduction. Fecundity and gonadosomatic index were assessed, and growth performance at different developmental stages was evaluated. The results indicated that both species possess a similar gonadosomatic index. The parent C. gariepinus possesses significantly (p < 0.05) higher male reproductive quality than C. macromystax. Fecundity was significantly higher (p < 0.05) in the female parent of C. macromystax and lower in C. gariepinus. The highest fertilization rates and hatching rates were achieved in the hybrid cross of ♀C. macromystax × â™‚C. gariepinus (♀Cm × â™‚Cg) which also recorded the lowest deformed larva rate. Survival rates at the larval stage were more than 80%, with the highest record of survival in the hybrid ♀Cm × â™‚Cg. However, survival rates in the fry stage were lower than 70%. The hybrid cross (C. macromystax × C. gariepinus) outperformed the parental cross of C. macromystax but was not significantly similar to the parental cross of C. gariepinus. The study revealed the potential of the hybrid ♀C. macromystax × â™‚C. gariepinus, and hybridizations of ♀C. macromystax × â™‚C. gariepinus (♀Cm × â™‚Cg) are indeed possible and proved to have a better growth and survival rate under semi-arid conditions, which would contribute significantly to the improvement of C. macromystax production in captivity.

The effect of calcium hydroxide addition on enhancing ammonia recovery during thermophilic composting in a self-heated pilot-scale reactor.

A modified outdoor large-scale nutrient recycling system was developed to compost organic sludge and aimed to recover clean nitrogen for the cultivation of high-value-added microalgae. This study investigated the effect of calcium hydroxide addition on enhancing NH3 recovery in a pilot-scale reactor self-heated by metabolic heat of microorganisms during thermophilic composting of dewatered cow dung. 350 kg-ww of compost was prepared at the ratio of 5: 14: 1 (dewatered cowdung: rice husk: compost-seed) in a 4 m3 cylindrical rotary drum composting reactor for 14 days of aerated composting. High compost temperature up to 67 °C was observed from day 1 of composting, proving that thermophilic composting was achieved through the self-heating process. The temperature of compost increases as microbial activity increases and temperature decreases as organic matter decreases. The high CO2 evolution rate on day 0-2 (0.02-0.08 mol/min) indicated that microorganisms are most active in degrading organic matter. The increasing conversion of carbon demonstrated that organic carbon was degraded by microbial activity and emitted as CO2. The nitrogen mass balance revealed that adding calcium hydroxide to the compost and increasing the aeration rate on day 3 volatilized 9.83 % of the remaining ammonium ions in the compost, thereby improving the ammonia recovery. Moreover, Geobacillus was found to be the most dominant bacteria under elevated temperature that functions in the hydrolysis of non-dissolved nitrogen for better NH3 recovery. The presented results show that by thermophilic composting 1 ton-ds of dewatered cowdung for NH3 recovery, up to 11.54 kg-ds of microalgae can be produced.

Effect of enzymatic pre-treatment on thermophilic composting of shrimp pond sludge to improve ammonia recovery.

In recent years, attempts have been made to develop a thermophilic composting process for organic sludge to produce ammonia gas for high value-added algal production. However, the hydrolysis of non-dissolved organic nitrogen in sludge is a bottleneck for ammonia conversion. The aim of this study was to identify enzymes that enhance sludge hydrolysis in a thermophilic composting system for ammonia recovery from shrimp pond sludge. This was achieved by screening useful enzymes to degrade non-dissolved nitrogen and subsequently investigating their effectiveness in lab-scale composting systems. Among the four hydrolytic enzyme classes assessed (lysozyme, protease, phospholipase, and collagenase), proteases from Streptomyces griseus were the most effective at hydrolysing non-dissolved nitrogen in the sludge. After composting sludge pre-treated with proteases, the final amount of non-dissolved nitrogen was 46.2% of the total N in the control sample and 22.3% of the total N in the protease sample, thus increasing the ammonia (gaseous and in-compost) conversion efficiency from 41.5% to 56.4% of the total N. The decrease in non-dissolved nitrogen was greater in the protease sample than in the control sample during the pre-treatment period, and no difference was observed during the subsequent composting period. These results suggest that Streptomyces proteases hydrolyse the organic nitrogen fraction, which cannot be degraded by the bacterial community in the compost. Functional potential analysis of the bacterial community using PICRUSt2 suggested that 4 (EC:3.4.21.80, EC:3.4.21.81, EC:3.4.21.82, and EC:3.4.24.77) out of 13 endopeptidase genes in S. griseus were largely absent in the compost bacterial community and that they play a key role in the hydrolysis of non-dissolved nitrogen. This is the first study to identify the enzymes that enhance the hydrolysis of shrimp pond sludge and to show that the thermophilic bacterial community involved in composting has a low ability to secrete these enzymes.

Inoculation of Neurospora sp. for improving ammonia production during thermophilic composting of organic sludge.

Recent attempts have been made to develop a thermophilic composting process for organic sludge to not only produce organic fertilizers and soil conditioners, but to also utilize the generated ammonia gas to produce high value-added algae. The hydrolysis of organic nitrogen in sludge is a bottleneck in ammonia conversion, and its improvement is a major challenge. The present study aimed to elucidate the effects of inoculated Neurospora sp. on organic matter decomposition and ammonia conversion during thermophilic composting of two organic sludge types: anaerobic digestion sludge and shrimp pond sludge. A laboratory-scale sludge composting experiment was conducted with a 6-day pretreatment period at 30 °C with Neurospora sp., followed by a 10-day thermophilic composting period at 50 °C by inoculating the bacterial community. The final organic matter decomposition was significantly higher in the sludge pretreated with Neurospora sp. than in the untreated sludge. Correspondingly, the amount of non-dissolved nitrogen was also markedly reduced by pretreatment, and the ammonia conversion rate was notably improved. Five enzymes exhibiting high activity only during the pretreatment period were identified, while no or low activity was observed during the subsequent thermophilic composting period, suggesting the involvement of these enzymes in the degradation of hardly degradable fractions, such as bacterial cells. The bacterial community analysis and its function prediction suggested the contribution of Bacillaceae in the degradation of easily degradable organic matter, but the entire bacterial community was highly incapable in degrading the hardly degradable fraction. To conclude, this study is the first to demonstrate that Neurospora sp. decomposes those organic nitrogen fractions that require a long time to be decomposed by the bacterial community during thermophilic composting.

Effect of Ca(OH)2 dosing on thermophilic composting of anaerobic sludge to improve the NH3 recovery.

The primary biological treatment method for organic sludge is composting and/or anaerobic digestion, but their product (compost or biogas) is of little economic benefit; therefore, an improved process to produce a high-value product is required to make sludge management more sustainable. Maximizing NH3 gas recovery during composting processes has the potential benefit of producing high-value microalgal biomass. However, the majority of produced ammonia does not evaporate as NH3 gas but retains as NH4+-N in the compost after fermentation. The present study investigates the effects of the timing of Ca(OH)2 dosing (on days 2, 5, and 9), and the Ca(OH)2 dose (1.1-2.6 mmol/batch), on lab-scale thermophilic composting of anaerobic sludge. The effects on NH3 recovery, organic matter degradability, and microbial activity are evaluated. Ca(OH)2 dosing immediately improved the emission of NH3, with yields 50-69% higher than those under control conditions. The timing of the dosing did not influence NH3 recovery or organic matter degradability. Higher Ca(OH)2 doses resulted in higher NH3 recovery, while microbial activity was temporarily and marginally inhibited. The pH of the compost reached 10-11.5 but quickly dropped to 8-8.5 within a day, probably because of neutralization of Ca(OH)2 by the emitted CO2 and release of NH3, which maintained the microbial activity. The present study indicated that Ca(OH)2 dosing would be useful to apply during thermophilic composting for NH3 recovery to cultivate high-value microalgal biomass, which enables this process to obtain a more economic benefit.

Effect of temperature on thermophilic composting of aquaculture sludge: NH3 recovery, nitrogen mass balance, and microbial community dynamics.

Development of thermophilic composting for maximizing NH3 gas recovery would enable the production of a nitrogen source which is free from pathogen/heavy metal, for the cultivation of high-value microalgae. The present study examined the effect of NH3 recovery, nitrogen mass balance, and microbial community dynamics on thermophilic composting of shrimp aquaculture sludge. The emission of NH3 gas at 60 and 70 °C was 14.7% and 15.6%, respectively, which was higher than that at 50 °C (9.0%). The nitrogen mass balance analysis revealed that higher temperatures enhanced the solubilization of non-dissolved nitrogen and liberation of NH3 gas from the produced NH4+-N. High-throughput microbial community analysis revealed the shift of the dominant bacterial group from Bacillus to Geobacillus with the rise of composting temperature. In conclusion, thermophilic composting of shrimp aquaculture sludge at 60-70 °C was the most favorable condition for enhancing NH3 gas recovery.

Serum cortisol level and survival rate of juvenile Epinephelus fuscoguttatus following exposure to different salinities.

BACKGROUND AND AIM: Brown-marbled grouper Epinephelus fuscoguttatus is a premium marine food fish with high demand in Asia. In fish, stress due to environmental changes such as fluctuations in the salinity can result in increased cortisol level. Stress in fish increases susceptibility to diseases ultimately resulting in death. Therefore, the aim of this study was to investigate the salinity tolerance of E. fuscoguttatus and their survival in lower salinities. MATERIALS AND METHODS: In this study, grouper juveniles (92.43±standard error of the mean 0.51 mm) maintained in 31 ppt seawater were transferred into five tanks with seawater diluted to 25, 20, 15, 10, and 5 ppt. The salinity of the control group was not changed and was maintained at 31 ppt. Serum cortisol was measured using ELISA at 0, 30, 60, and 120 min after the fish were transferred to the different concentrations of salinity. RESULTS: The survival percentage was recorded for 14 days following the transfer and the results revealed that serum cortisol of fish in a high change in salinity (15, 10, and 5 ppt) was significantly higher than the control group immediately after exposure. At the high salinity change, the cortisol levels gradually decrease at 30 min and 60 min, until no difference in cortisol concentration was observed at 120 min. No mortality was observed in fish exposed to low salinity change (25 and 20 ppt) while in higher salinity change (5 ppt), the survival percentage was 50%. CONCLUSION: The study revealed that the serum cortisol concentration was high initially and continues to decrease to resting cortisol level at 120 min indicating that cortisol hormone is released following acute stress as a primary response in grouper juveniles.

Effects of pristine polyvinyl chloride fragments on whole body histology and protease activity in silver barb Barbodes gonionotus fry.

Silver barb Barbodes gonionotus fry were exposed to polyvinyl chloride (PVC) fragments at increasing concentrations of 0.2, 0.5 and 1.0 mg/L for 96 h, following which whole body histological evaluation and analysis of the digestive enzymes trypsin and chymotrypsin were performed. Whole body trypsin and chymotrypsin activities increased significantly in fish exposed to 0.5 and 1.0 mg/L PVC as compared those exposed to zero or 0.2 mg/L PVC. In fish exposed to all tested concentrations, PVCs were observed in both the proximal and distal intestine, and fish exposed to 0.5-1.0 and 1.0 mg/L PVC, respectively, and these particles were associated with localized thickening of the mucosal epithelium. No tissue damage was evident in any other internal organs or gills. This lack of damage may be attributed to the absence of contaminants associated with the PVC fragments and their relatively smooth surface. The increased whole body trypsin and chymotrypsin activities may indicate an attempt to enhance digestion to compensate for epithelial thickening of the intestine and/or to digest the plastics.