I.
Introduction
Water is a fundamental resource for
all forms of life on Earth. From drinking and sanitation to agriculture and
industry, water plays an indispensable role in human survival and socioeconomic
development. However, with the rapid pace of industrialization, urbanization,
and population growth, water pollution has emerged as a major global concern
[1,2]. The discharge of untreated or inadequately treated wastewater into
rivers, lakes, and groundwater sources has led to the degradation of water quality,
posing severe risks to both environmental and human health [3,4].
In many developing countries,
including India, a significant portion of domestic, agricultural, and
industrial wastewater is released directly into natural water bodies without
proper treatment [5,6]. This wastewater often contains harmful substances such
as suspended solids, organic and inorganic compounds, heavy metals, pathogens,
and dissolved salts [7,8].
Conventional wastewater treatment
technologies, such as sedimentation, coagulation-flocculation, membrane
filtration, and reverse osmosis, are effective but often involve high capital
and operational costs [9,10]. This makes them unaffordable or impractical in
low-income and rural settings, creating a pressing need for low-cost,
efficient, and environmentally friendly alternatives [11,12]. In recent years,
there has been growing interest in using agricultural waste materials as
low-cost adsorbents for wastewater treatment [13]. One such promising material
is Rice Husk Ash (RHA)—a by-product obtained after the combustion of rice husk,
which is the outer protective covering of rice grains [14]. India, being one of
the largest producers of rice in the world, generates millions of tons of rice
husk annually, a large portion of which is either burned or discarded,
contributing to air pollution and land degradation [15].
This project holds significance on
multiple fronts. It promotes the use of agricultural waste (rice husk) as a
value-added product, thus reducing the environmental footprint of both
agriculture and wastewater treatment sectors [16]. The materials used—rice husk
ash, sand, gravel, and low-cost sensors—are affordable and locally available,
making the system economically accessible to low-income communities [17]. The
simple design of the filtration unit can be easily scaled up or down depending
on the application, from household use to community-based water treatment
centers. The project also serves as an educational tool to raise awareness
about water pollution, sustainable practices, and the importance of water
quality monitoring [18]. By integrating a TDS sensor, the project bridges
traditional filtration methods with modern technology, enabling smart water
purification systems that are self-regulating and transparent [19].
Rice husk, when burned under
controlled conditions, yields rice husk ash rich in silica (SiO₂) and other
metal oxides. This ash possesses high surface area, porosity, and excellent
adsorption capabilities, making it suitable for removing a variety of
contaminants such as heavy metals (lead, chromium, cadmium), dyes, and even
organic matter [20]. Moreover, RHA is abundant, renewable, biodegradable, and
inexpensive, aligning perfectly with the principles of sustainable development
and circular economy.
II.
Materials
and Methods
2.1 Sample Collection
Wastewater samples were collected
from seven ponds in Raipur, India: (Fig.1)
Budha Pond, Telibandha Lake, Katora Pond, Raja Pond, Chhatva Pond, Vyas
Pond, Shitala Pond. (Fig.2)
Fig.
1: Map of Raipur
(Chhattisgarh) India.
Fig. 2: Sample Collection site at Raipur Chhattisgarh
India
2.2 Methodology
Rice husks were first collected,
thoroughly washed to remove dirt and trimmed impurities, then air-dried. The
dried husks were combusted in an open-air setting to produce rice husk ash
(RHA), which was subsequently sieved into a fine powder and stored in airtight
containers to preserve its adsorptive properties [21]. Ground Ocimum sanctum
leaves (Tulsi) were mixed with the RHA powder at a defined ratio (e.g., 5–10%
w/w) to incorporate its antimicrobial properties (2). This composite serves as
the active media in a vertical filtration column prepared by layering the
RHA–Tulsi blend atop inert support material. Wastewater was introduced from the
top of the column under gravity flow, and filtered effluent was collected at
the base. Multiple column configurations were tested—varying RHA/Tulsi ratios
and layer thicknesses—to optimize filtration performance according to
contaminant type (e.g., heavy metals, microbial load) (3). RHA’s high amorphous
silica content (typically >80%) provides a large specific surface area and
porous structure, enabling effective adsorption of pollutants like phenols,
heavy metals, and dyes (4). The added Tulsi functions as a natural biocide: its
bioactive compounds exhibit bactericidal activity against waterborne pathogens
at concentrations ≥500 mg/L (5). During filtration trials, influent and
effluent samples were analyzed for turbidity, heavy metal concentration (Fe,
Pb, Cd), phenolic compounds, and total bacterial counts to evaluate removal
efficiencies. The combined adsorptive and antimicrobial properties of the
RHA–Tulsi bed are anticipated to achieve high contaminant removal while
maintaining an eco-friendly, low-cost filtration system (Fig.3).
Fig. 3: rice husk based filter using at different
situations (a) tap filter for urban area (b) cascade filter for high volume
water (c) cloth filter for rural area
II.
Results
Water-quality parameters were measured before and after treatment across seven ponds (A–G): The pH increased across all ponds, shifting from acidic levels
between 5.62 and 6.94 before treatment to neutral or slightly alkaline values
ranging from 6.11 to 8.21 afterward. This neutralization effect aligns with prior
findings where rice husk–based filters raised pH toward safe drinking standards
(~6.5–8.5). TDS has marginal reductions (~2–6%), with
post-treatment levels ranging from 8.99 to 90.12 mg/L across all ponds. Similar
studies involving rice husk-based filtration often report modest TDS declines,
reflecting minimal dissolution of ash constituents and consistent removal of
particulate-bound ions rather than extensive ionic reduction.
Conductivity in the ponds decreased
modestly by approximately 2–5%, mirroring the slight reduction in TDS
(8.99–90.12 mg/L). Since electrical conductivity is directly proportional to
dissolved ion concentration, this small drop indicates that the rice husk ash
and Tulsi filter primarily removed particulates rather than dissolved salts.
Turbidity dropped sharply in all
ponds: Pond A (18.2 → 5.0 NTU, ~72%), Pond B (9.7 → 2.1 NTU), Pond C (5.6 →
1.1 NTU), and Ponds D–G consistently achieved 1.0–2.3 NTU, reflecting robust
clarity gains. These results lignwith prior studies reporting up to 95% NTU
reduction using rice husk ash filters.Rice husk ash treatment transformed
previously “disagreeable” pond water into “agreeable” in terms of both color and odor, achieving clear,
odor-free conditions across all samples. Adsorption studies confirm RHA’s
efficacy in removing colorants and odor-causing organics, consistent with
similar water purification applications.
Bacterial presence was eliminated in
all treated ponds. The rice husk ash filter bed achieved up to 96% bacterial
removal in field conditions, confirming an effective biocidal and adsorption
mechanism. Laboratory studies also demonstrate that rice husk ash can trap and
inactivate bacteria like S. aureus.
IV.
Discussion
pH
Adjustment
The increase in pH to
neutral–slightly alkaline levels (6.11–8.21) reflects the buffering and
mineral-leaching action of rice husk ash (RHA), which is rich in silica and
some alkali metals. Similar trends have been reported: washed RHA has elevated pH post-filtration into acceptable
drinking ranges (6.5–8.5) Maintaining pond water within the optimal 6.5–9.0
range is crucial for aquatic life health and biological treatment processes.
TDS
& Conductivity
The slight decreases in TDS and conductivity align with data from composite RHA filters, which
often result in modest increases or decreases depending on ash-mineral
interactions . In these trials, the addition of Ocimum sanctum likely
contributed minimal ionic load, and overall mineral uptake restrained TDS/EC
changes—consistent with acceptable environmental levels.
Turbidity
Removal
The ∼80–90% turbidity reduction across ponds is notable. For
example, Pond A achieved ∼72%,
while others reached >80%. Laboratory work with washed RHA reports >95%
turbidity removal at moderate dosages This excellent performance here confirms
that the RHA–Tulsi composite effectively adsorbs suspended solids. The presence
of amorphous silica in RHA (up to ~98%) provides extensive surface area for
flocculation and particulate trapping.
Color
& Odor
Filter training results showed
treated water becoming both colorless
and odor-neutral, shifting to
"agreeable" across all ponds. This is consistent with reports from
biosand filters and RHA systems, which effectively remove chromogens and odor-causing
compounds via adsorption.
Microbial Elimination
Complete removal of bacterial
presence across all treated samples points to a strong biocidal effect. This likely stems from two mechanisms: physical
trapping within RHA pores, and the antimicrobial action of Tulsi—rich in
polyphenols like eugenol—and slow-drip filtration that further reduces
microbial viability. RHA filters have achieved >90% bacteria removal in
other studies, and biosand analogues exhibit up to 99% removal.
Fig.
4: Effect of Ocimum Sanctum merged RHA in turbidity
removal of seven pond water.
Synergistic
Performance of RHA–Tulsi Composite By leveraging the dual action of RHA’s adsorptive capacity and Tulsi’s antibacterial properties,
thiscomposite material demonstrates broad-spectrum treatment effectiveness (Fig
4).
Physical
removal of turbidity and color via coagulation and adsorption. Buffering of pH into the ecologically
safe 6.5–9.0 range. Microbial
disinfection, likely enhanced by Tulsi’s antimicrobial compounds. Minimal mineral leaching, evidenced by
stable TDS and conductivity(Table 1).
These
results align with literature indicating that natural adsorbents such as RHA
support multistage treatment gains. The study’s use of open-environment burnt RHA (as opposed to high-temperature
incineration) suggests that simple, low-cost processing still yields effective
treatment media (Fig 5 and Fig. 6).