Technology's Role In Solving Water Pollution

Water pollution is a pressing issue that threatens ecosystems, wildlife, and human health. With industrialization, urbanization, and agricultural activities on the rise, our water sources are increasingly vulnerable to contamination by chemicals, plastics, and waste. To address this crisis, innovative technologies are being developed to provide access to clean drinking water and mitigate the devastating consequences of water pollution.

One such technology is the LifeStraw, a small, inexpensive microfiltration device that removes 99.9% of waterborne bacteria. Weighing just 2 ounces, it is highly portable and can filter up to 264 gallons of water. Another example is the SE200 Community Chlorine Maker, which uses electrolysis to produce chlorine from water, salt, and electricity, effectively killing bacteria.

In addition, the Desolenator, a solar desalination tool, removes 99% of contaminants from water, producing roughly 15 liters of freshwater per day. With a lifespan of 20 years, it offers a sustainable solution for water-stressed communities. Warka Water, a 30-foot tower that collects drinking water by condensing dew, provides a biodegradable and tool-free solution that can be set up in less than a week.

Advanced technologies like nanotechnology and filtration systems are also proving effective in removing heavy metals and pollutants. Additionally, algae-based treatments use natural processes to absorb contaminants.

To address water scarcity, technologies like the WaterSeer, which pulls moisture from the air to produce clean drinking water, and the Janicki Omni Processor, which creates drinking water from human feces, show promising results.

The adoption of these technologies, along with sustainable practices and community involvement, is crucial in the fight against water pollution to protect our planet's most vital resource.

Nanotechnology and filtration systems can remove heavy metals and other pollutants from water

Nanotechnology and filtration systems offer effective solutions for removing heavy metals and pollutants from water. Nanomaterials, such as carbon-based nanomaterials, zero-valent metals, metal-oxide-based nanomaterials, and nanocomposites, can be employed to eliminate heavy metals from water due to their unique characteristics, including a large surface area and the ability to be modified.

The removal of heavy metals from water can be achieved through various techniques, including adsorption, ion exchange, chemical precipitation, and membrane technology. Adsorption involves using materials like activated carbon to attract and trap pollutants, while ion exchange replaces unwanted ions in the water with other ions. Chemical precipitation converts pollutants into solid particles by adding chemicals, and membrane technology uses selective barriers to remove pollutants.

Functionalization of nanomaterials can enhance their separation, stability, and adsorption capacity. This can be achieved by modifying their surfaces with molecules like biomolecules, polymers, or inorganic materials. The specific functionalization method depends on the type of nanomaterial and the desired outcome.

The efficiency of nanomaterials in removing heavy metals is influenced by factors like pH, temperature, contact time, initial heavy metal concentration, and adsorbent dosage. Optimizing these parameters is crucial for maximizing the removal of heavy metals from water.

Algae-based treatments use natural processes to absorb contaminants

The quorum sensing (QS) molecules play a crucial role in the algal-bacterial population dynamics. QS is a population-dependent interaction mechanism in bacterial cells that is facilitated by the exchange of small signalling molecules, which helps in coordinating gene expression and performing ecological functions. The QS molecules produced by bacteria can also stimulate algal lipid synthesis and increase algal productivity.

The algal-bacterial interaction may exhibit mutualism, commensalism, and parasitism. Mutualism is a process where both species benefit from each other. For example, bacteria can supply vitamin B12 to microalgae, and in exchange, microalgae can supply fixed carbon to the bacteria. In a commensalism type of relationship, one of the species benefits while the other is neither harmed nor benefitted. In parasitism, one species benefits at the expense of the other.

The algal-bacterial systems can be categorised into two types: suspended growth and attached growth systems. Suspended growth systems include open and closed bioreactors, such as high rate algal ponds (HRAPs) and photobioreactors (PBRs). Attached growth systems include algal turf scrubbers (ATS) and membrane aerated biofilm reactors (MABRs).

The physio-chemical factors that affect the interaction between algae and bacteria include pH, temperature, light intensity, nutrients, and external aeration. For most microalgal species, the ideal pH for growth is between 7 and 9, and the optimum temperature range is 20-30°C. Light intensity and light/dark cycle duration also play a significant role in algal-bacterial systems, as they influence algal photosynthesis, nitrification, and the formation of settleable algae-bacterial granules.

Algal-bacterial systems have the potential to remove micropollutants through sorption, biodegradation, and photodegradation. Sorption is the process of transferring a compound from an aqueous phase to a solid phase, and it depends on the properties of the compound and the solid surface, as well as environmental conditions such as pH, temperature, and ionic strength. Biodegradation is the process where enzymes break down the pollutants, and photodegradation uses light energy to break down the pollutants into their component parts.

Harvesting methods for algal-bacterial systems include mechanical, chemical, electricity-based, or biological means. Bio-flocculation is a harvesting method that occurs due to the interactions between algae-bacteria, algae-fungi, and algae-algae, and it has advantages such as zero toxicity, higher efficiencies, and less energy consumption.

The algal-bacterial biomass grown during wastewater treatment can be converted into valuable products and biofuels through biochemical or thermochemical conversion. Biochemical conversion includes transesterification, fermentation, and anaerobic digestion, while thermochemical conversion involves processes such as hydrothermal liquefaction and pyrolysis.

Constructed wetlands act as natural filters, cleaning polluted water

Constructed wetlands are an innovative and natural solution to water pollution. They are shallow, flat water bodies that fill and drain during rainfall, acting as natural filters. This process is facilitated by carefully selected and positioned plants that act as a sieve, filtering and capturing sediment and fine particles, as well as slowing the flow of wastewater.

The roots of these plants are integral to the process, binding accumulated sediments, which can remove up to 90% of the sediments in runoff or streamflow. As well as this, the settling of sediments in wetlands improves water quality by removing pollutants such as heavy metals, which are often attached to soil particles.

Constructed wetlands also aid in the removal of excess nutrients such as nitrogen and phosphorus, which can be taken up by wetland plants and stored in less harmful chemical forms. This process prevents the overstimulation of plant, algae, and cyanobacteria growth, which can produce toxic chemicals and choke out natural vegetation and wildlife.

Constructed wetlands are so effective at removing excess nutrients that they are often specifically built to treat effluent from secondary sewage treatment plants.

Advanced Oxidation Processes (AOPs) use high-energy light or radical species to break down pollutants

Advanced Oxidation Processes (AOPs) are a group of advanced technologies that use high-energy light or radical species to break down pollutants into their component parts. AOPs rely on the in-situ production of highly reactive hydroxyl radicals, which are the strongest oxidants that can be applied in water. These reactive species are formed with the help of one or more primary oxidants (e.g. ozone, hydrogen peroxide, oxygen) and/or energy sources (e.g. ultraviolet light) or catalysts (e.g. titanium dioxide).

AOPs are particularly useful for cleaning biologically toxic or non-degradable materials such as aromatics, pesticides, petroleum constituents, and volatile organic compounds in wastewater. The contaminant materials are converted to a large extent into stable inorganic compounds such as water, carbon dioxide and salts, i.e. they undergo mineralization.

The AOP procedure is used for removing contaminants from wastewater coming out of several types of heavy industries, including the petrochemical and plastic industry, food processing industry, pharmaceutical industry, metal and metal plating industry, and textile and dying industry.

AOPs have several advantages over biological or physical processes, including unattended operation with a very small footprint, the absence of secondary wastes (sludge), and the ability to handle fluctuating flow rates and compositions.

The main process steps are as follows:

• Sedimentation of suspended solids or filtration depending on the level of TSS (Total Suspended Solids)
• PH adjustment if necessary, usually determined after a feasibility test in the lab
• AOP Electro-catalytic reactor
• DAF or Lamella clarification. At this stage 30-60% of COD is reduced.
• AOP catalytic oxidation in either a tank or an underground pit (optional)
• Post-filtration to remove any suspended catalyst particles. At this stage, the liquid is clear with minimal or no colour with 75-90% COD reduction.
• AOP Photo-catalytic UV or UV + Hydrogen Peroxide or Ozonation alone or a combination of these to achieve 95% to 100% COD removal.

AOPs represent an alternative drinking water treatment option to other processes such as air stripping, GAC adsorption, and resin sorption. AOPs destroy primary organic contaminants directly in water through chemical reactions, whereas air stripping and sorption are phase-transfer processes that physically transfer organic contaminants to a gas or solid phase.

AOPs can also be used for disinfection purposes. Several AOP technologies — namely ozonation, ozonation combined with H2O2, and certain types of UV irradiation — are currently used for disinfection in the water treatment industry.

The mechanism of hydroxyl radical production depends on the type of AOP technique that is used. For example, ozonation, UV/H2O2 and photo catalytic oxidation rely on different mechanisms of hydroxyl radical generation:

• UV/H2O2: H2O2 + UV → 2·OH (homolytic bond cleavage of the O-O bond of H2O2 leads to formation of 2·OH radicals)
• Ozone-based AOP: O3 + HO- → HO2- + O2 (reaction between O3 and a hydroxyl ion leads to the formation of H2O2 (in charged form))
• O3 + HO2- → HO2· + O3-· (a second O3 molecule reacts with the HO2- to produce the ozonide radical)
• O3-· + H+ → HO3· (this radical gives to ·OH upon protonation)

Membrane technologies use a permeable barrier to remove pollutants from water

Membrane technology uses a permeable barrier to remove pollutants from water. Membranes are used to facilitate the transport or rejection of substances between mediums, and the mechanical separation of gas and liquid streams. Membrane technology is commonly used in industries such as water treatment, chemical and metal processing, pharmaceuticals, biotechnology, the food industry, as well as the removal of environmental pollutants.

Membranes can be classified as isotropic or anisotropic. Isotropic membranes are uniform in composition and physical structure, while anisotropic membranes are non-uniform over the membrane area and are made up of different layers with different structures and composition.

There are four main types of pressure-driven membrane processes: microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. The main difference exhibited by these processes, apart from their pressure requirements, is their membrane pore sizes.

Membrane modules are large membrane areas packaged economically into specific types, such as plate and frame modules, tubular modules, spiral wound modules, and hollow fiber modules.

Membrane fouling occurs when suspended solids, microbes, organic materials, etc. are deposited on the membrane surface or within the membrane pores, thereby causing decreased permeate flux. Methods to reduce fouling broadly fall under pretreatments, membrane modification, fluid management, or effective cleaning.

Frequently asked questions