The simultaneous removal of methylene blue (MB) and Ca2+ by recyclable adsorbents based the scales derived from coal gasification system.

The transformation of solid wastes from industrial production into effective adsorbents could significantly contribute to wastewater treatment. In this study, after acidizing and burning soft scale (SS) from coal gasification system, two magnetic adsorbents (mag-ASS and mag-BASS) were prepared via the combination of magnetite with ultrasonic, respectively. The treatment effects of mag-ASS and mag-BASS were then investigated for simulated wastewater containing macromolecular organic matter [i.e., methylene blue (MB)] and Ca2+. The results indicated that the pseudo second order kinetic, Elovich, Freundlich, Langmuir and Temkin model could well describe the adsorption behavior of MB and Ca2+ onto mag-ASS and mag-BASS. The maximum adsorption capacities of mag-ASS for MB and mag-BASS for Ca2+ were 600.53 mg/g and 102.54 mg/g, respectively. Surprisingly, the adsorption abilities of mag-ASS for MB and mag-BASS for Ca2+ show significantly higher than the others. The adsorption mechanisms of MB mainly included electrostatic interaction, π-π conjugate interaction and cation exchange, while those of Ca2+ were mainly electrostatic interaction and cation exchange. The diffusion of MB and Ca2+ onto the magnetic adsorbents might be controlled by the combined effects of intraparticle and liquid film diffusion. There was no significant reduction in adsorption capacity after 8 cycles of adsorption and desorption, indicating that SS-based magnetic adsorbents had good recyclability and stability. Moreover, the removal efficiency of mag-BASS for total hardness and total organic carbon in real coal gasification gray water (CGGW) was 82.60 and 64.10%, respectively. The treatment of CGGW and the resource of wastes would significantly promote the reasonable disposal of coal gasification scales.

Novel insights into aerobic duration control-based partial nitritation in source-separated blackwater treatment: Growth type, inoculation source, and comammox threat.

Aerobic duration control (ADC), whereby aeration is terminated before nitrite is extremely oxidized during the nitrification process, is an effective strategy to achieve partial nitritation (PN) for blackwater. This study evaluated the effects of microbial growth type, influent ammonia-oxidizing organisms (AOO), and comammox bacteria from seeding sludge to ADC-based PN. The long-term operation of lab-scale reactors and model simulations were implemented to select the best growth type. The biofilm formed on the inner wall of the activated sludge reactor decreased the nitrite accumulation ratio (NAR) from 99.2% to 77.2%. Meanwhile, the NAR of the pure-biofilm reactor decreased from 95.9% to 47.8%. The deteriorated PN of the biofilm-related reactors was due to the extended solid retention time and increased substrate saturation constants of AOOs compared with those of nitrite-oxidizing organisms (NOO). Periodic biofilm carrier regeneration and biofilm thickness control can recover PN performance but are difficult to implement. In contrast, the optimized activated sludge reactor exhibited high (NAR >94%) and stable (>3 months) PN performance when treating real blackwater. Nitrifiers were found in blackwater, and chemically enhanced high-rate activated sludge pretreatment removed more NOOs than AOOs (41.8% vs. 24.3%) and increased the influent AOO/NOO ratio. Interestingly, the influent AOOs supported fast PN start-up in the moving-bed biofilm reactor without the initial inoculation of activated sludge. Moreover, model simulations verified that high and stable PN could also be realized in an activated sludge reactor by the continuous inoculation of influent AOOs, which is a novel PN start-up strategy. Metagenomic analyses showed that the comammox bacteria from the seeding sludge eventually disappeared owing to their intrinsic specific growth rates and free ammonia inhibition. The findings of this study will provide insightful guidelines for PN application in decentralized and semi-centralized wastewater treatment systems.

Full-scale semi-centralized wastewater treatment facilities for resource recovery: operation, problems and resolutions.

The first full-scale semi-centralized wastewater treatment and resource recovery system based on source separation was implemented from 2014. To assess the operation performance, operating costs and resolve the problems faced in this system, the latest operation data from April 2017 to September 2018 was investigated. The results show that greywater and blackwater modules exhibited good removal performance for organics and nutrients, although misconnection between pipelines existed and influent loading rates fluctuated. The effluent could meet reuse standards. The biogas production rates of raw sludge could reach 7.27-10.9 m3 gas·per cubic raw sludge. The specific cost of treated water was higher than in a conventional treatment system. Power consumption made a major contribution to the total cost with a proportion of 55.3-94.2%. After optimizing and considering the comprehensive efficiencies, the costs would be affordable. The dewatered sludge of the anaerobic digestion module has been applied to agricultural and landscaping soil. It is suggested that organics in blackwater could be recovered as volatile fatty acids with high-efficiency anaerobic fermentation and used as an external carbon source for short-cut biological nitrogen removal. In conclusion, the semi-centralized system will be a feasible and sustainable alternative for conventional treatment systems in future.

Carbon capture for blackwater: chemical enhanced high-rate activated sludge process.

Blackwater has more benefits for carbon recovery than conventional domestic wastewater. Carbon capture and up-concentration are crucial prerequisites for carbon recovery from blackwater, the same as domestic wastewater. Both chemical enhanced primary treatment (CEPT) and high-rate activated sludge (HRAS) processes have enormous potential to capture organics. However, single CEPT is subject to the disruption of influent sulfide, and single HRAS has insufficient flocculation capacity. As a result, their carbon capture efficiencies are low. By combining CEPT and HRAS with chemical enhanced high rate activated sludge (CEHRAS) process, the limitations of single CEPT and single HRAS offset each other. The carbon mineralization efficiency was significantly influenced by SRT rather than iron salt dosage. An iron dosage significantly decreased chemical oxygen demand (COD) lost in effluent. Both SRT and iron dosage had a significant influence on the carbon capture efficiency. However, HRT had no great impact on the organic mass balance. CEHRAS allowed up to 78.2% of carbon capture efficiency under the best conditions. The results of techno-economic analysis show that decreasing the iron salt dosage to 10 mg Fe/L could promise profiting for blackwater treatment. In conclusion, CEHRAS is a more appropriate technology to capture carbon in blackwater.