RESOURCE RECOVERY FROM WASTEWATER, SOLID WASTE AND WASTE GAS: ENGINEERING AND MANAGEMENT ASPECTS Evaluation of groundwater hardness removal using activated clinoptilolite Weixing Liu 1,2 & Rajendra Prasad Singh 1,2 & Saravanan Jothivel & Dafang Fu 1,2 Received: 17 April 2019 /Accepted: 9 August 2019 # Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Current study aimed to investigate modified natural clinoptilolite for removal of calcium and magnesium from the groundwater. Feasibility of clinoptilolite for groundwater hardness removal in production and operation was verified by static adsorption experiment and the experiment of fixed bed and degasification column. Subsequently, the main parameters for groundwater treatment using clinoptilolite were also explored. Results show that in the process of clinoptilolite in adsorption is dominant reaction process. The adsorption equilibrium time was unchanged when the hardness of raw water changes from 450 to 550 mg/ L. With respect to comparative analysis of price and performance, NaCl found to be the most suitable clinoptilolite regenerated agent. The adsorption efficiency was high when the residence time was 20–25 min in the pilot experiments. The reaction mechanism was mainly substitution reaction according to ion equilibrium, and the treatment capacity of the degasifier combined with the fixed bed was 20% higher than that of with only fixed bed. Keywords Groundwater . Hardness . Activated zeolite . Adsorption . Degasifier Introduction Current population exploitation and rapid infrastructure devel- opment are expected to put additional pressures on water re- sources (Rivas and Nonhebel 2016). Whereas, decrease in groundwater table and increase in the thickness of the vadose zone lead to a longer recharge cycle of groundwater, a longer path for surface runoff to recharge groundwater. An increase in the dissolved amount of minerals in the recharge water results in an increase in the groundwater hardness (Cucchi et al. 2008). Excessive exploitation of groundwater causes change in the hydrodynamic as well as hydro-geochemical conditions of the aquifer, which is prone to the dissolution of calcium (Ca 2+ ) and magnesium (Mg 2+ ), leading to the increase in hardness (Malana and Khosa 2011; Sheikhy Narany et al. 2018). At present, the softening methods of groundwater mainly include agent softening method, membrane softening method, and ion exchange method. Ion exchange method is widely used in industrial water desalination, and the use of more softeners for ion exchange resin (Luo et al. 2018). However, in the batch processing of drinking water, the application of ion exchange method is negligible. The possible reason is that ion exchange resin is a fragile organic matter, which will cause a certain threat to health when applied to drinking water. At the same time, resin is mostly used to remove organic matter (Levchuk et al. 2018). Zeolite is a good ion exchange agent, and it is mainly used in the field for water treatment, specifi- cally for ion adsorption, organic adsorption, and ammonia nitrogen adsorption (Krstic et al. 2018; Wen et al. 2018). Many studies have proved that zeolite can significantly improve its adsorption properties and remove a variety of metal ions after pretreatment and modification. He et al. (2016) indicated that the coal fly ash-prepared zeolite could be used as an effective adsorbent for the removal of heavy metal ions from aqueous solution. Kong et al. (2017) noted that zeolite-supported microscale zero-valent iron can be used to remove the permeability reaction barrier of Cd 2+ and Pb 2+ Responsible editor: Philippe Garrigues * Dafang Fu fdf@seu.edu.cn 1 School of Civil Engineering, Southeast University, Nanjing 211189, China 2 Southeast University-Monash Joint Research Centre for Future Cities, Nanjing 211189, China Environmental Science and Pollution Research https://doi.org/10.1007/s11356-019-06193-9