7 June 2018
Cleaning Up Using Waste
Bio-plastic from wastewater sludge
Our cities produce massive amounts of wastewater. This wastewater – from homes, factories, mills – undergoes treatment at wastewater treatment plants. And, as a result, sludge is formed.
Responsible disposal and management of the tonnes and tonnes of wastewater sludge thus formed, remains a major problem. What if we could use the treated wastewater sludge to address another major environmental concern?
The sludge from water treatment plants contains a variety of microorganisms capable of synthesising polyhydroxyalkanoates. Bacteria store carbon and energy as polyhydroxyalkanoates.
In the past, scientists used polyhydroxyalkanoates to synthesise an environment friendly form of plastics. In order to replace plastics derived from fossil fuel with plastics from polyhydroxyalkanoates, microbes need to be cultured on a large scale which would not be economically viable. Sludge from urban wastewater treatment plants, on the other hand, is a readily available, inexpensive resource.
Scientists from the Indian Institute of Technology and the Jawaharlal Nehru University, Delhi came up with a way to improve the yield of such biocompatible plastics from the sludge formed after treatment of municipal wastewater.
“We realized that, in order to make the process cost-effective, it is essential to find the optimum conditions at which the maximum amount of polyhydroxyalkanoates could be extracted from treated wastewater sludge” says Indu Shekhar Thakur, JNU. The team, therefore, used statistical techniques to determine parameters such as the temperature, sludge solids concentration and duration of extraction for maximum yield.
“We followed it up with lab studies”, says Manish Kumar, JNU. The researchers then collected liquid sludge samples from a municipal wastewater treatment plant at New Delhi. In the laboratory, they solidified, cooled, dried and prepared the sludge for a polyhydroxyalkanoate isolation reaction at statistically optimised conditions. “The results matched our predictions”, beams Pooja Ghosh from IIT Delhi.
Polyhydroxyalkanoate yield increased significantly when reaction conditions were numerically optimised. “Not only that, the extraction resulted in a rich diversity of polyhydroxyalkanoates”, says Indu Shekhar Thakur, JNU.
These researchers have found a way to use statistical tools to minimise the cost of producing biodegradable plastic. In doing so, they simultaneously address the problem of wastewater sludge disposal as well as that of replacing non-biodegradable plastic with biodegradable plastics.
Bioresour. Technol., 255: 111-115
3 November 2017
New Model for Water Treatment
Worldwide, water resources are contaminated with various organic micropollutants. Besides conventional water treatment, we now have an advanced process of degrading such contaminants involving oxidation by hydroxyl radicals. But to optimise this process, we need models which can predict the reaction rate parameters of organic contaminants in water.
Recently, Shikha Gupta from the NBRI and Nikita Basant from the ETRC, Lucknow, proposed a model based on the relationship between the physicochemical properties of organic compounds and their reactivities towards the hydroxyl radicals.
Using PaDel software, they calculated the molecular descriptors that affect the reactivities of the molecules towards the hydroxyl radical in aqueous medium.
Statistically selecting the “best fit”, they chose a method of calculating the electronegativity of carbon atoms based on their atomic volume. The topological polar surface area of the molecules was calculated based on functional groups. The team also factored in average molecular weight, number of double bonds, and number of halogen atoms.
They used a large data set of reaction rate parameters for diverse organic compounds. Then they randomly split the data set into training set and validation set. The training set was utilized for model development, while the validation set was used to assess the predictivity of the model.
To develop the model, the researchers used a decision tree boost approach in which the software processes the data and makes decisions in a branching manner.
The scientists confirmed the predictive ability of the model using new random test data.
This model covers diverse chemical classes and has broader applicability than previous models. It can provide reliable estimates of the reactivities of new and emerging micropollutants towards hydroxyl radicals without prior experimental data and can, therefore, be employed in water purification systems.
Chemosphere, 185: 1164-1172 (2017)
1 November 2017
Using ecofriendly ZnO nano-rods
Dyes colour our world. Unfortunately, dyes are not eco-friendly. Methods to degrade them are a hot spot of research all around the world. One way to deal with the problem is by using nanomaterials.
Recently, researchers from the Siddaganga Institute of Technology, Tumakuru reported tackling the problem with zinc oxide nanoparticles produced using the juice of Chakkota, Citrus maxima.
They mixed the chakkota juice, an oxidising agent, and zinc nitrate, the reducing agent, in different concentrations. The scientists found that heating the mixture at 400℃ in a furnace for five minutes was optimum for the reaction. They examined the surface morphology of the particles using a scanning electron microscope and found that the ZnO nanoparticles are one-dimensional nanorods.
These nanorods show photocatalytic activity, speeding up the reaction in the presence of light. This property was used by the scientists to degrade dyes which work on redox potentials. They used methylene blue, a staining dye, as their sample. In the presence of light and the ZnO nanorods, the dye was degraded, releasing hydroxyl ions. This was observable as a decrease in the intensity of blue colour.
The scientists suggest that this simple, ecofriendly method for degrading dyes can be applied in dye and textile industries to process the effluents released.
Spectrochim. Act. 185: 11-19 (2017)
28 October 2017
Tamiraparani river basin
The Tamiraparani river originates on the eastern slopes of the Western Ghats, about 2,000 m above mean sea level. It runs for about 125 km before it meets the Bay of Bengal. But it drains an area of nearly six thousand square kilometers. Over the last few centuries, many dams and channels were built for irrigation. Over 20 million litres of water are used for drinking purposes.
Image: Karthikeyan.pandian via Wikimedia Commons
A team of researchers from the Anna University, Chennai and the Manonmaniam Sundaranar University, Tirunelveli, were concerned. They suspected that the contamination of groundwater in this region might be due to agricultural and industrial activities. To ensure the supply of safe drinking water, careful monitoring of drinking water sources is essential.
They conducted a survey to examine this issue. They took groundwater samples from 124 wells in the Tamiraparani river basin in southern India. And analysed the pH, electrical conductivity, total dissolved solids and salinity of the samples using a portable water quality meter. Based on electrical conductivity and total dissolved solids, the scientists say that around two percent of the groundwater is in a critical condition.
The researchers also performed trace element analysis by Inductively Coupled Plasma Atomic Emission Spectroscopy – an analytical technique used for the detection of trace metals. The trace element analysis showed that more than six percent of the samples exceeds the permissible limit. The traces of iron, manganese and lead are found to be considerably higher than the standard level. However, there is no health risk associated with the present status of the water bodies.
The scientists suggest that the contaminated wells should be treated with rainwater to reduce contamination. Rainwater harvesting near water bodies might be a feasible solution.
Water contamination in the Tamiraparani river basin is below the critical limit recommended by the WHO. Analysis of water sources is an important step to monitor and to ensure safety. This survey acts as a baseline for similar activities by universities in other parts of India.
Chemosphere, 185: 468-479 (2017)
Hair Dyes as Pollutants
Detoxification by microbes
Hair dyes mask age, make us look young and attractive. But when we wash the dye off, it enters water bodies. Hair dyes contain a mixture of chemicals including p-phenylenediamine, a genotoxic chemical – it harms animals, including humans. Once the dye enters water, it is hard to remove without spending energy.
Last fortnight, Swati and Mukesh from the Haldia Institute of Technology, West Bengal and Sudarson from the Tel Aviv University, Israel found a solution: bioremediation. They searched for dye degrading bacteria in salon effluent. They cultured the bacteria using sugarcane bagasse powder – a commonly available and cheap source of nutrient medium. The team then tested bacteria, isolated from the effluent, for their ability to decolourise hair dye. Using a UV-visible spectrophotometer, they measured the degree of decolourization.
And among the isolates, they found an Enterobacter species, which can degrade hair dye. Molecular techniques confirmed that the isolate is Enterobacter cloacae. Using a well-diffusion assay, they found that the bacteria break dye down to eco-friendly residual products.
The harm that our fascination for artificial hair colour does to the environment can now be overcome by using commensal bacteria from our gut.
J. Hazardous Materials, 338: 356-363 (2017)