Rice husk biochar removes fluoride from groundwater, prevents drinking water contamination, new study shows

Prolonged fluoride consumption in higher concentrations in drinking water can cause dental fluorosis, skeletal fluorosis, kidney diseases, arthritis

By Prabhakar Sharma, Rakesh Kumar
Published: Tuesday 07 March 2023

India is an agrarian country, with agriculture occupying 60 per cent of its land, and as the economy expands, farmers are expected to feed a growing population while also increasing exports. 

Water is a vital resource in practically all industrial, agricultural and urban applications. This is what has increased the necessity of water for irrigation throughout the years, and in the lack of strong regulations, fresh water supplies across the country have been overexploited. 

Groundwater, extracted with tube wells and hand pumps, is the most important source for drinking and cooking in rural India. Blind extraction encourages groundwater contamination with several pollutants, mainly geogenically. 

In Bihar, for instance, groundwater in the rural areas of 31 out of 38 districts have high concentrations of arsenic, fluoride and iron, constituting a serious health risk. Fluoride, one of the pollutants in groundwater, is primarily caused by geological processes but is also contributed through anthropogenic activities across India. 

Prolonged fluoride consumption in higher concentrations in drinking water can cause dental fluorosis, skeletal fluorosis, kidney diseases and arthritis. Dental fluorosis, or brown stains on the teeth caused by weakened enamel, is one of the most noticeable symptoms due to fluorosis. 

Skeletal fluorosis is somewhat more difficult to identify unless significant deformation occurs and typically requires radiographic testing. Thus, it may not be as prominent as dental fluorosis. For 4,157 habitats over 98 blocks in 11 districts of Bihar, the level of fluoride in the groundwater is alarmingly high. 

Besides, crop residue management is also challenging in Bihar and across India, as farmers willingly or unwillingly burn the residue on farms. 

To tackle both the problems with one solution, a group of researchers from Nalanda University focuses on the ‘waste-to-energy’ approach to remove fluoride from groundwater. 

The team led by Prabhakar Sharma from the school of ecology and environment studies, Nalanda University, Rajgir, Bihar, investigated the potential of renewable biochar produced from rice husk biomass to absorb fluoride pollutants from groundwater. 

Rice husk is generally used as fuel in households. The scientists studied the role of rice husk-modified biochar in treating fluoride-contaminated surface and groundwater under varying solution chemistry, co-existing ions and biochar-amended through column transport experiments. The results were published in the journal Environmental Technology & Innovation.

Surface and groundwater samples collected from Rajgir reported removal efficiencies at actual alkaline pH conditions. A comparative analysis for fluoride-contaminated water using modified biochar showed that fluoride removal was achieved under the World Health Organization and Bureau of Indian Standards permissible limits than raw biochar. 

Hand pumps and tube wells are generally used as the source of potable water for drinking and cooking, according to the report. Thus, biochar-mediated sand columns can be used for defluoridation. 

Fluoride remediation using biochars showed significant removal at neutral pH and illustrated how practical these biochars and techniques are for defluoridation, which can be efficiently implemented, said Rakesh Kumar, research scholar of the School of Ecology and Environment Studies at Nalanda University. 

Fluorosis results from excessive fluoride intake from various sources, including food, water, air (due to gaseous industrial waste), and excessive use of toothpaste. 

With respect to its physical and chemical nature, biochar for wastewater treatment has demonstrated various benefits in agricultural production and soil reclamation. Due to discrete composition and physiochemical properties, subsurface environmental media are heterogeneous and complex, resulting in unreliable transport and deposition behavior for biochar and other colloids. 

The deposition and co-transport of rice husk-modified biochar and fluoride were analysed at pH 7 in column experiments to replicate this technique in biochar-mediated sand filters in hand pumps and tube wells. Low-cost biochar production is a topic that is receiving more and more attention from government regulatory agencies and the general public. 

Raw and modified biochars can be employed for in-situ applications in treating surface and groundwater at high pH (alkaline conditions), co-occurring ions and under varying salt strengths at a commercial scale, the study showed. 

Besides, column fixed-bed saturated experiments can be applied to sand-based filtration units in wastewater treatment plants, riverbank treatment and soil amendment. This study analysed biochars in different salt strengths at pH 7. So, it is recommended to consider higher concentrations and mimic solutions for real problems. 

Generally, fluoride levels may vary significantly from one hand pump to another hand pump in the same village within a range of a few kilometers due to unseen and unpredictable aquifers. Fluorosis impacts individual children differently based on their dietary intake. 

Their social marginalisation has resulted from fluoride in addition to the impairment it causes. The government must promote cheaper, more accessible household-level filtration techniques so that households have a remedy for serious health problems.

Views expressed are the authors’ own and don’t necessarily reflect those of Down To Earth.

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