Prof BD Tripathi

Vertical greenery systems can combat urban air pollution - November 2016

Air pollution has become a great threat to urban areas of developing countries. The main causes of increase in the level of air pollution are increasing population, urbanization and industrialization. Urban air often contains high levels of pollutants that are harmful to human health and well being. The role of green plants in air pollution attenuation is well known, but urban construction is replacing huge areas of vegetation with concrete buildings and low albedo surfaces. The resulting changes in the thermal properties of surface materials and the lack of proper evapotranspiration in urban areas lead to the urban heat island (UHI) effect. Greenery should be reintroduced into such urban landscapes by bringing nature back into the city.

Vertical greenery system (VGS) means growing of plants directly on or with the help of plant guiding constructions alongside the building façade. Green façades generally involve use of woody or herbaceous climbers, algae, lichens and small shrubs. These can be planted directly into the ground or in pots or planter boxes and some other structures to anchor the plants. Along with green roofs, sky gardens and residential gardens, VGSs can also be used for air pollution attenuation. Green roofs are also known for cooling overlying air masses relative to a conventional roof. Residential gardens are major portion of the urban green space and play an important role in the conservation of biodiversity and aesthetic beauty of urban areas.

Sky gardens are of great ecological, economical and social importance, but very few studies have been done in India on green roofs, Vertical greenery systems or sky gardens. Choosing appropriate plants for urban landscapes is essential to avoid possible financial and environmental losses and thus the Air Pollution Tolerance Index (APTI) can be a good tool to select best plant species. The air pollution tolerance index (APTI) is based on four major biochemical properties of leaves which are ascorbic acid, relative water content, total chlorophyll and leaf extract pH. A plant’s tolerance to air pollutants varies with these parameters. Chlorophyll content decreases due to production of Reactive Oxygen Species (ROS) in the chloroplast under water stress. Presence of higher ascorbic acid content in leaves might be a strategy to protect thylakoid membranes from oxidative damage under such water stress conditions, as ascorbic acid is involved in the defence against ROS produced by the photosynthetic apparatus. Few works have been done on the APTI of various tree species in Varanasi; anticipated performance index based on APTI for green belt development was also analyzed. Deposition of particulate matter on climber vegetation on living walls has been quantified.

The APTI of some climbers were also estimated in India, but systematic study is rather lacking for the development of vertical gardens and green roofs by using particular climber plants based on their APTI. Increasing motor vehicle emissions and decreasing green space have created an imbalance in the air quality. Thus, it is necessary to develop VGSs on buildings to compensate for the loss of natural vegetation in the process of urbanization. Climbers can be grown directly in the ground with a support to develop green façade or they can also be grown in pots or planter boxes. Loamy soil with good drainage is considered good for most of the climbers.

Climbers can be grown according to different situations. Quisqualis indica, Antigonon leptopus and Adenocalymma comosum can be grown in sunny conditions. Similarly, Clerodendrum splendens can be grown in partial shade. Heavy climbers like A. leptopus, Bignonia magnifica, Beaumontia grandiflora, Hiptage benghalensis, Quisqualis magnifica and Clerodendron splendens grow vigorously and cover large area and thus they are suitable choice for development of VGS. Some of these plants such as, C. splendens, Q. indica and Adenocalymna calycina can also be grown on pergola. Climbers can add to air pollution attenuation along with higher plants, along with that, they can also increase the aesthetic value of a building. Factors such as soil type, availability of sunlight, and adequate nutrients to plants, proper irrigation, and proper support for plants to grow should also be considered for development of VGSs. Annual maintenance will promote plant survival and proper growth of plants.

Unplanned urban expansion and urban sprawl in Varanasi has resulted in dense settlements with little green space in the core areas of the city. Varanasi is a compact sub-tropical city which is characterized by tall buildings and narrow roads which results in the city canyon-like structure. Thus, air pollutants are not dispersed properly and remain in surrounding ambient air for longer durations. Removal of such pollutants can be easily achieved with the help of vertical greenery system on building walls. Much building wall and rooftop surface area can be used to develop roof top gardens and vertical greenery systems in the city. Therefore it is necessary to evaluate the APTI of selected climber plants that could be used to develop VGSs.

Thus, in order to attenuate air pollution and bring other ecosystem services; APTI of commonly available climber species of plants was evaluated by a group of scientists led by myself so that those with a higher tolerance can be recommended for use in VGSs in the Varanasi city.

Further, air quality was monitored at seven sites to assess the status of pollution, based on which two sites were selected for evaluating APTI. The predominant wind direction for the study area is towards west (Fig. 1). Twenty eight climber plant species commonly found near a polluted site (site-1) were selected and their APTI was evaluated. APTI of same set of plants were also analyzed at relatively less polluted rural site (site-7) for comparative study. Linear regression analysis has revealed a high positive correlation between APTI and ascorbic acid content (R2 = 0.8676) and positive correlation between APTI and Chlorophyll content (R2 = 0.4957). On the basis of higher APTI values (greater than 17), eleven climber species i.e. Ipomoea palmata, Antigonon leptopus, Thunbergia grandiflora, Clerodendrum splendens, Aristolochia elegans, Quisqualis indica, Vernonia elaeagnifolia, Petrea volubilis, Adenocalymma comosum, Cryptolepis buchanani and Jacquemontia violacea have been identified at polluted urban site to develop vertical greenery systems in this compact tropical city. The present study has implications for mitigating and reducing adverse health impacts from persistent exposure to air pollutants while also providing regulating ecosystem services thereby improving the local urban ecology. This research work was very well recognized by its publication in an international journal ‘Landscape and Urban Planning, (2015); 144; 119–127’ and highly appreciated by the scientific community.

Treating wastewater by using modified biosorbent - September 2016

The increased discharge of metals into the aqueous environment as a result of various industrial processes is considered serious environmental threat because of their toxic, non-biodegradable and bio-accumulative nature. Among the metal pollutants, Chromium(VI) and Nickel(II) have been recognized as high priority toxic pollutants because of their mutagenic and carcinogenic effects even at low concentrations. The anthropogenic sources of chromium and nickel includes various industrial processes such as leather tanning, electroplating, refining, welding, steel manufacturing, pulp processing, wood preservation etc. Considering the toxicity of these metals to natural ecosystems and human beings, the Bureau of Indian Standard has established the industrial effluent maximum permissible discharge limit of Cr(VI) and Ni(II) into inland surface water as 0.1 mg L-1 and 3.0 mg L-1 respectively (BIS, 1993). Therefore, treatment of effluents laden with Cr(VI) and Ni(II) ions prior to discharge into receiving aqueous environment is necessary.

Several separation techniques such as chemical precipitation, electrochemical treatment, flotation, ion exchange, membrane filtration, reverse osmosis, sedimentation and solvent extraction are available and documented for the removal of these toxic metals. However, these techniques suffer from various technical and economical limitations to remove toxic metals in the low concentration range of 1 to 100 mg L-1. Thus, it is essential to develop simple, cost-effective and environment friendly technology for the remediation of toxic metals from wastewater. Recently, removal of metals using biosorption technique has gained significant interest because of their high effectiveness at low concentrations, economic viability and environment friendly nature. 

Biosorption can be defined as the ability of biological materials to accumulate heavy metals from wastewater through metabolically mediated or physico-chemical pathways of uptake. Algae, bacteria, fungi and yeasts have proved to be potential metal biosorbents. The major advantages of biosorption over conventional treatment methods include:  low cost; high efficiency; minimisation of chemical and biological sludge; no additional nutrient requirement; regeneration of biosorbent; and  possibility of metal recovery.

The biosorption process involves a solid phase (sorbent or biosorbent; biological material) and a liquid phase (solvent, normally water) containing a dissolved species to be sorbed (sorbate, metal ions). Due to higher affinity of the sorbent for the sorbate species, the latter is attracted and bound there by different mechanisms. The process continues till equilibrium is established between the amount of solid-bound sorbate species and its portion remaining in the solution. The degree of sorbent affinity for the sorbate determines its distribution between the solid and liquid phases. The present attempt is in continuation to our earlier biosorption experiments, which confirmed the superiority of the Fenton modified Hydrilla verticillata dried biomass (FMB), in removing Cr(VI) and Ni(II), from aqueous solutions as well as from wastewater in batch mode (Hydrilla verticillata is a hardy, rapidly growing fresh water grass that pulls in essential nutrients from rich lakebed soils.  It has a mild, mineral wateresque and sometimes peppery taste).

The biosorption results obtained from previous batch experiments were useful in providing information about the efficacy of metal-biosorbent systems. However, the data obtained under batch experiments are usually not applicable to most of the column processes where contact time is not long enough to achieve equilibrium. Thus, it becomes necessary to determine the practical applicability of the FMB in a continuous column practice.

Therefore, experiments were carried out to investigate the potential of FMB in removing Cr(VI) and Ni(II) ions in a continuous up-flow packed-bed column.

The FMB was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy coupled with energy dispersive X-Ray spectroscopy. Continuous flow packed bed column studies were carried out in a glass column with an internal diameter of 4 cm and length 35 cm. Schematic diagram of lab-scale column set-up is given in Fig. 1.

Effects of different packed-bed column parameters such as bed height, flow rate, influent metal ion concentration and particle size were examined. The outcome of the column experiments illustrated that highest bed height (25 cm); lowest flow rate (10 mL min-1), lowest influent metal concentration (5 mg L-1) and smallest particle size range (0.25-0.50 mm) are favourable for biosorption. The maximum biosorption capacity of FMB for Cr(VI) and Ni(II) removal were estimated to be 89.32 and 87.18 mg g-1 respectively. The breakthrough curves were analyzed using Bed Depth Service Time (BDST) and Thomas models. The experimental results obtained agree to both the models. Column regeneration experiments were also carried out using 0.1 M HNO3. Results revealed good reusability of FMB during ten cycles of sorption and desorption. Performance of FMB-packed column in treating secondary effluent samples was also tested under identical experimental conditions. Results demonstrated that the FMB packed column removed more than 90% of Cr(VI) and Ni(II) ions after the biosorption process. This cost-effective and promising technology was very well recognized in its publication in an international journal “Ecotoxicology and Environmental Safety, 132 (2016) 420-428” and has been well received by the scientists.

The uniqueness of Hydrilla

Hydrilla is what's known as a freshwater tape grass, meaning that it's got a similar genetic makeup as its super food cousins like wheat and barley grass, but instead of growing in drier climates (relatively speaking), it thrives in lakes, streams and semi-saline estuaries. This is important for two reasons: grasses in general are easily some of the most nutritious foods known to man, hence their massive popularity as dietary supplements over the last few decades and their ability to be the sole food source of massive, thousand-pound animals like horses and cows. However, Hydrilla's unique aquatic root structure gives it an advantage that wheat and other dry land grasses don't have: it can siphon minerals, vitamins, and other essential nutrients from the phenomenally rich lakebed soils in which it grows, which have a distinctly different composition than those above ground. This endows Hydrilla with a very unique nutritional profile that few other foods can match.

Few know this, but Hydrilla verticillata is actually the richest food source of calcium on the planet and is similarly abundant in a host of mineral cofactors such as chromium, selenium, iron, magnesium, zinc and silica. It's also a potent vegan source of the notoriously rare vitamin B12, as well as the rest of the B-Vitamin family, again having some of the highest concentrations of any food currently known to man. Like all whole foods, the nutrients found in Hydrilla are bound to naturally occurring carbohydrates, proteins and polyphenols in organic molecular complexes in the ideal form for human digestion and metabolism, meaning that when you consume Hydrilla your body actually absorbs and assimilates the nutrients therein (unlike the synthetic vitamins and minerals found in the majority of supplements, which cannot be fully utilized by cells). This is also in large part due to the fact that Hydrilla is phenomenally rich in a wide range of enzymes, which help the body further digest and assimilate the plant. Further research has shown Hydrilla contains a wide range of polysaccharides, widely recognized in the medical community for their immune- and general health-enhancing properties, and a rare type of molecule known as otteliones A and B, which have been shown in studies to have potent anti-tumour effects.