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Sludge treatment by Earthworm-Enhanced reed beds towards smart-cities

Publication . Gholipour, Amir; Duarte, Elizabeth Fernandes de Almeida; Fragoso, Rita do Amaral; Galvão, Ana Fonseca

This study explored an innovative approach for sewage sludge management using sludge treatment reed bed (STRB) enhanced with earthworms (W-STRB). To the authors’ knowledge, it was the first evaluation of STRB with earthworms under temperate climate (Portugal). The research included experiments in Beirolas wastewater treatment plant (pilot-scale) and Horto greenhouse at ISA (bench-scale). Beirolas pilot-scale was assessed for one year of feeding (24 cycles, mean sludge loading rate (SLR): 43.59 ± 14.49 kg of dry solids (DS) per m2.year) and 132 days of final resting. Four types of units were tested including planted unit with earthworms (WP), planted unit without earthworms (P), without plant with earthworms (W) and control unit without plants and earthworms (C), all replicated. In Beirolas pilot-scale, the plant species was Arundo donax and the earthworm was Eisenia fetida. In Horto bench-scale, two plant species were tested, Arundo donax and Phragmites australis. Planted units included Eisenia fetida earthworms and an additional unit without plants or earthworms was used as control. The bench-scale was studied for six months of feeding (50, 60, and 70 kg.DS.m-2.year-1) and two months of resting. Beirolas experiment showed that DS of all units were over 70 % while volatile solid content (VS) reached the minimum content at 53 % in the WP unit indicating higher stabilization in the presence of earthworms. A synergistic impact of earthworms could also increase plant biomass production by 30 % in the WP unit compared to the P unit. The WP unit showed significant reduction in the release mass (g) of pollutants in the drained water. The WP unit reduced 10 % the mass of heavy metal in the residual sludge compared to the P unit. The study emphasized earthworms’ positive role in STRB, and potential reuse of the residual sludge contributing to circular economy in smart cities.

2024-10-28Doctoral thesis

Open access

Evaluating drained water quality in a pilot worm-sludge treatment reed bed planted with Arundo donnas in the Mediterranean climate

Publication . Gholipour, Amir; Fragoso, Rita; Galvão, Ana; Duarte, Elizabeth

This study evaluated the impact of incorporating earthworms (Eisenia fetida) on the drained water quality from a sludge treatment reed bed. The experiment encompassed four setups of treatment beds in two replicates: planted with Arundo donax and addition of earthworms, planted without earthworms, unplanted with earthworms, and treatment bed without plants nor earthworms as control. The units were fed every two weeks with mixed sewage sludge, a blend of primary and secondary sludge over 24 cycles. The mixed sewage sludge had mean dry and volatile solid contents of 24.71 g.DS.L 1 (± 13.67) and 19.14 g.VS.L 1 (± 10.29) resulting a sludge loading rate of 43.59 kg.DS.m 2.year 1 (± 14.49). The inclusion of earthworms in the planted unit reduced release masses of total suspended solids, chemical oxygen demand, nitrate and phosphorous by 43, 45, 75 and 45 % compared to the planted unit. Plant biomass production increased by 43 % with the earthworm presence. The removal effi- ciency of the units improved after a ramp-up phase (after six months feeding) of which the concentration of TSS, COD and Escherichia coli met limits for water reuse while nitrogen components and phosphorous surpassed the limits. The planted unit with earthworms removed 99 and 99 % of TSS and COD, respectively. Overall, water loss namely through evapotranspiration and earthworm hydration need, positively correlated with pollutant con- centration, and earthworm-planted unit had 46 % higher water loss compared to control unit

2024-06Journal article

Open access