Sludge Treatment Reed Bed under different climates: A review using meta-analysis

Water balance analysis in a novel pilot-scale of the Worm-sludge treatment reed bed (W-STRB) planted with Arundo donax

A one-year study of sludge treatment reed bed assisted with earthworms (W-STRB) was conducted in a temperate climate. The effects of using Eisenia fetid and Arundo donax on W-STRB water balance (WB) and dewatering efficiency (DE) were investigated. Four different bed configurations were tested: worm-planted (WP), planted (P), worm-control (W), and control (C), duplicated resulting in a total of eight units. The beds received a total of 24 cycles of mixed sewage sludge twice per month (average loading rate: 43.59 kg.DS. m-2.year-1). It was found seasonal variation played a significant role in WB and DE. During the dry season, the thickness of the residual sludge (RS) layer was less than 1 cm, with a dry solid (DS) content of over 80%, in contrast, the wet season indicated an increase in RS thickness to nearly 30 cm (DS < 15 % for all units). The WP unit exhibited the lowest RS accumulation, 22% less than the P, W, and C units. The subsurface layer had a 5% lower volatile solids (VS) content compared to the surface layers. After 132 days of a final resting, WP unit had the highest RS volume reduction of 65 % (DS = 71 % and VS = 53 %) and a RS thickness of 6 cm indicating a 10 % higher stabilization compared to P unit. The population of earthworms was 30% higher in the WP unit compared to the W unit. As the subsurface DS exceeded 20 % during the dry season, the population increased. The WP unit showed a 43% higher above-ground plant biomass compared to the P unit. In WB analysis, evapotranspiration (ET) was 46% higher in the WP unit (average daily ET = 5.44 mm in the dry season). The main process of water loss was through drainage and Awhile water content in RS layer was 57 % during feeding period. The water percolation rate of all units decreased by 99%, particularly during the wet season, reaching less than 0.1 m.day-1.

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.