Effect of passive ventilation on the performance of unplanted sludge treatment wetlands: heavy metal removal and microbial community variation

A study of pilot sludge treatment reed beds for sludge dewatering and treatment under a hot and arid climate

In the effort to identify sustainable sludge management options, pilot-scale sludge treatment reed beds (STRBs) were tested and assessed in the Sultanate of Oman in the first integrated experimental study of this nature-based solution in the Middle East region. A total of 18 pilot STRB units were established and monitored for almost 2 years; half were planted with native Phragmites australis reed species, and half served as unplanted control units. Employing a randomized complete block design, the study examined varying sludge loading rates (SLR) of 75, 100, and 125 kg/m2/year. Results underscored the effectiveness of STRBs in reducing the sludge volume, with observed reductions reaching 98.0% of the applied sludge volume, particularly prominent in the SLR75 units. During the final resting phase, the STRBs showed slightly higher concentrations of total Kjeldahl nitrogen (TKN) and total phosphorus (TP) compared to the unplanted beds, while maintaining concentrations lower than those of the applied activated sludge. Furthermore, heavy metal concentrations were consistently diminished in the STRBs compared to the unplanted beds, aligning with the established national and international standards for sludge reuse in agricultural contexts. The results of this study provide the first valuable insight into the potential of STRBs as an effective, sustainable, and climatically suitable approach for sludge dewatering. Specifically, an SLR of 100 kg/m2/year is proposed as an optimum loading rate for the hot and arid Middle East climate. This study advances our understanding of STRBs as a pivotal component in the realm of arid-region sludge treatment, shedding light on their capacity to facilitate enhanced dewatering, mineralization, and nutrient removal, thereby contributing to the broader discourse on sustainable waste management practices.

Simultaneous removal of heavy metals and bioelectricity generation in microbial fuel cell coupled with constructed wetland: an optimization study on substrate and plant types

A microbial fuel cell coupled with constructed wetland (CW-MFC) was built to remove heavy metals (Zn and Ni) from sludge. The performance for the effects of substrates (granular activated carbon (GAC), ceramsite) and plants (Iris pseudacorus, water hyacinth) towards the heavy metal treatment as well as electricity generation was systematically investigated to determine the optimal constructions of CW-MFCs. The CW-MFC systems possessed higher Zn and Ni removal efficiencies as compared to CW. The maximal removal rates of Zn (76.88%) and Ni (66.02%) were obtained in system CW-MFC based on GAC and water hyacinth (GAC- and WH-CW-MFC). Correspondingly, the system produced the maximum voltage of 534.30 mV and power density of 70.86 mW·m^-3, respectively. Plant roots and electrodes contributed supremely to the removal of heavy metals, especially for GAC- and WH-CW-MFC systems. The coincident enrichment rates of Zn and Ni reached 21.10% and 26.04% for plant roots and 14.48% and 16.50% for electrodes, respectively. A majority of the heavy metals on the sludge surface were confirmed as Zn and Ni. Furthermore, the high-valence Zn and Ni were effectively reduced to low-valence or elemental metals. This study provides a theoretical guidance for the optimal construction of CW-MFC and the resource utilization of sludge containing heavy metals.

Sustainable Dewatering of Industrial Sludges in Sludge Treatment Reed Beds: Experiences from Pilot and Full-Scale Studies under Different Climates

Sludge treatment reed beds (STRBs) are an established sludge treatment technology with multiple environmental and economic advantages in dewatering sludge generated during domestic wastewater treatment. However, little is reported regarding their appropriateness and efficiency for the treatment of sludge produced during industrial wastewater treatment and from water works. These sludge types may have significantly different quality characteristics than typical domestic sludge and may contain constituents that could affect their dewaterability. Therefore, the dewatering of these industrial sludge types is usually tested in small-scale pilot STRBs before the construction of full-scale systems. This paper presents and summarizes the state-of-the-art experience from existing pilot and full-scale STRB systems from various countries and climates treating sludge from various industrial sources, evaluates the suitability and the advantages of this sustainable treatment technology, and proposes the required dimensioning for efficient full-scale STRB operation and performance.