Injection of hydrogen gas stimulates acid mine drainage treatment in laboratory‐scale hydroponic root mats

Abstract

The environmentally benign disposal of acid mine drainage (AMD) is still a technical challenge. In the present study, artificial AMD was treated in a laboratory‐scale floating hydroponic root mat of soft rush, Juncus effusus. This ecotechnological system was operated with hydrogen injection and water recirculation but without an external carbon supply. It achieved a mean increase of ΔpH = 3.3 up to pH ≈ 8.2, high sulfate removal of up to 87%, and efficient removal of iron (100%), aluminum (99.8%), manganese (97.4%), and zinc (99.6%). Sulfide was not detected in the outflow. Treatment performance correlated with the amount of hydrogen loading. Daily oscillations of the redox potential up to amplitudes of ΔEh ≈ 450 mV in a mean range of Eh ≈ −150 to +300 mV indicated a correlation of plant physiology and removal processes. Apparently, sulfate and metal removal were the result of chemolithotrophic microbial sulfate reduction supported by the externally provided H2 and chemoorganotrophic sulfate reduction driven by rhizodeposits. Bicarbonate generated in the microbial transformation of such plant‐derived organic carbon contributed to pH neutralization. The effluent's pH increase was governed further by recirculation of the treated AMD. The flow regime and the injection of hydrogen at the ground of the root mat caused concentration gradients where the most efficient removal occurred in the deepest zone of the root mat. Further investigations should target long‐term stability, plant growth dynamics, load variations, balances of carbon and sulfur, the removal of H2S and metal precipitates from the system as well as efficient hydrogen supply.

Floating Wetlands: A Sustainable Tool for Wastewater Treatment

“…Constructed floating wetlands [27] Floating island [23,47] Floating treatment wetlands [11,25,28,[38][39][40][41]49,50,[58][59][60] Artificial floating beds [48] Floating island system [19] Floating beds [43] Floating bioplato [61] Hydroponic root mats [44] www.advancedsciencenews.com www.clean-journal.com sorption and sedimentation processes. [17,63,68] A few plant species such as helophytes release atmospheric oxygen into the rhizosphere.…”

“…Juncus effuses and Pontederia cordata TN: 15.7%, nitrate and nitrate-nitrogen: 20.6%, ammonia-nitrogen: 51.1%, TP: 47.7%, and OP: 79% [50] Urban wastewater Field scale Tech-IA floating element each having rectangular lattice shape, made from ethylene-vinyl acetate Iris pseudacorus NO 3 -N: 82%, NH 4 -N: 20%, COD: 13%, and BOD 5 : 5% [25] Storm water Field scale Floating mat was made of ethylene-vinyl acetate…”

“…The commercial application of FTWs was first seen for the remediation of eutrophic lakes in Germany and for rivers in Japan . Currently, they are being used to treat hypertrophication, sewage and domestic wastewater, combined sewer overflow, contaminated groundwater, stormwater, acid mine drainage, poultry effluent, piggery effluent, boron enriched water, polluted river water, and nutrients enriched water . Recently, plant–bacteria partnerships have been exploited in FTWs for the maximum remediation of contaminated water .…”

Diverse and abundant arbuscular mycorrhizal fungi in ecological floating beds used to treat eutrophic water

“…Ecological oating bed (EFB) is a promising ecological engineering tool for restoring polluted (eutrophic [27][28][29], organic polluted [30], heavy metals polluted [31] and so on) waterbodies. It has many advantages, including small land occupied, little in uence by water level uctuation, convenient management, economical and e cient, and also with a good landscape effect [32].…”