Experimental Study for Sand Filter Backwash Water Management: Low-Cost Treatment for Recycling and Residual Sludge Utilization for Radium Removal

Abstract

Management of backwash water (BW) generated from sand filtration of groundwater naturally contaminated with iron (Fe), manganese (Mn), and radium (Ra) remains a challenge worldwide. The present study investigated the effectiveness of a low-cost clay ceramic filter for BW recycling along with residual sludge utilization for Ra removal from BW. A 15 day continuous ceramic filtration process operated at a constant flux of 2000 L/m2/d (83 LMH) showed 99% removal of Fe, Mn, and turbidity. The treated BW was found suitable for recycling back to the sand filters. Subsequently, the residual sand filter backwash sludge (BS) was collected, characterized by scanning electron microscopy (SEM) and X-ray diffraction, and examined as a potential adsorbent to the Ra. Results showed that the sludge constituted heterogeneous basic elements, with higher percentages of iron and manganese oxides. The sludge can be classified as typical mesoporous and poorly crystalline minerals consisting primarily of quartz and Mn2O3. Over 60% of Ra from the initial 2.1 bq/L could be removed by sludge in 30 min at neutral pH. The adsorption kinetics of sludge described well by the pseudo-second order model and Ra adsorption on the sludge were mainly controlled by chemisorption rate-controlling steps, intraparticle diffusion, and external mass transfer processes. Treatment of BW by low-cost clay ceramic filters and the utilization the BS for Ra removal would be a sustainable sand filter BW management practice.

Recirculation of Backwash Water in the Water Treatment Plant for the Needs of the Combined Heat and Power Plant

“…Underground water treatment plants generate backwashings of a relatively unchanged composition, characterized by a significant content of iron and manganese compounds [Shafiquzzaman et al 2021] and the presence of bacteria which influences the catalytic removal of manganese, iron and ammonia. The composition of the backwashings produced at the surface water treatment plants is strongly correlated with the quality of the abstracted water, which changes throughout the year.…”

“…It usually involves the removal of contaminants by sedimentation [Kučera and Hanušová, 2018], which can be accelerated by dosing lime and polyelectrolytes [Petris et al 2019, Arendze and Sibiya 2014, Kuś and Koźmiński 1993]. Increasingly, ultra and microfiltration is also used to purify the recycled filter backwashings, it is an expensive solution, so it is recommended to use other equally effective but low-cost alternatives [Shafiquzzaman et al 2021]. Depending on the processes used for purifying backwash water, the main indicators of their quality could even meet the requirements of drinking water [Shafiquzzaman et Currently, the reuse of spent backwash water by returning it to the water treatment line is a popular solution in the world, but the rules for its implementation and operation are not regulated by legal provisions.…”