K.M. Manjaiah

Simultaneous removal of multiple pesticides from water: Effect of organically modified clays as coagulant aid and adsorbent in coagulation–flocculation process

Contamination of drinking water sources with agrochemical residues became a major concern in the twenty-first century. Coagulation–flocculation is the most widely used water-treatment process, but the efficiency to remove pesticides and other organic pollutants are limited compared to adsorption process. Thus, simultaneous action of adsorption on normal bentonite or organo-modified montmorillonite clays [modified with octadecylamine (ODA-M) and octadecylamine + aminopropyltriethoxysilane (ODAAPS-M)] followed by coagulation–flocculation by alum and poly aluminium chloride has been evaluated for removal of 10 different pesticides, namely atrazine, lindane, metribuzin, aldrin, chlorpyriphos, pendimethalin, α-endosulphan, β-endosulphan, p, p′-DDT, cypermethrin and two of its metabolites, endosulphan sulphate and p, p′-DDE, from water. The coagulation without integration of adsorption was less effective (removal % varies from 12 to 49) than the adsorption–coagulation integrated system (removal % varies from 71 to 100). Further, coagulation integrated with adsorption was more effective when organically modified montmorillonite was used as adsorbent compared to normal bentonite. The removal efficiency of organic clay depends upon the concentration of pesticides, doses of clay minerals, and efficiency was more for ODAAPS-M as compared to ODA-M. The combination of ODAAPS-M-clay with coagulants was also used efficiently for the removal of pesticides from natural and fortified natural water collected and the results exhibit the usefulness of this remediation technique for application in water decontamination and in treatment of industrial and agricultural waste waters.

Exploitation of Nano-Bentonite, Nano-Halloysite and Organically Modified Nano-Montmorillonite as an Adsorbent and Coagulation Aid for the Removal of Multi-Pesticides from Water: A Sorption Modelling Approach

The objective of this study was to investigate the removal of multi-pesticides through a combined treatment process with coagulation–adsorption on nano-clay. Nano-clays like nano-bentonite, nano-halloysite and organically modified nano-montmorillonite were used as the adsorbent, and alum and polyaluminium chloride (PAC) were used as the coagulants. The coagulation method alone was not sufficient to purify water, whereas coagulation plus adsorption methods provided superior purification. Amongst the nano-clays used, organically modified nano-montmorillonite gave the best result in terms of pesticide removal from water. In order to evaluate the effect of coagulant addition on the removal efficiency of nano-clay, the respective adsorption isotherms were also calculated in the presence and absence of coagulants. Freundlich isotherm constants have shown that adsorption of pesticides on different nano-clay depends on the type of clay, presence and absence of coagulants as well as the properties of pesticides. The treatment combination having the maximum removal capacity was used efficiently for the removal of pesticides from natural and fortified natural water. The results indicated that alum–PAC coagulation aided by nano-clay as an adsorbent was the superior process for the simultaneous removal of multi-pesticides from water.

Removal of Poly Aromatic Hydrocarbons (PAHs) from Water: Effect of Nano and Modified Nano-clays as a Flocculation Aid and Adsorbent in Coagulation-flocculation Process

Water treatment process involving simultaneous action of adsorption on different nano and organo-modified nano-clays followed by coagulation-flocculation by alum and poly aluminium chloride (PAC) has been evaluated for the removal of PAHs (naphthalene, acenaphthalene, phenanthrene, fluoranthene, anthracene, and pyrene) from water. When clay minerals along with alum and PAC were used for treatment, 37.4–100.0% removal of PAHs was observed compared to 20–38% removal using normal water treatment process with either alum or alum + PAC. The effectiveness of clay minerals for removal of PAHs followed the order (P < 0.05): halloysitenano-clay (HN-clay) < normal bentonite (NB-clay) < hydrophilic nano-bentonite (HNB-clay) < nano-montmorillonite modified with dimethyl dialkyl amine (DMDA-M-clay) ≈ nano-montmorillonite modified with octadecylamine and aminopropyltriethoxysilane (ODAAPS-M-clay) ≈ nano-montmorillonite modified with octadecylamine (ODA-M-clay) in combination with alum + PAC. The modified treatment process (alum + PAC + clay minerals), where water was initially treated with clays followed by normal process of coagulation (alum + PAC), was found to be the most effective method with maximum removal for ODAAPS-M-clay (97.7–100.0%) which is at par wih ODA-M (97.0–100.0%), and DMDA-M-clay (94.8–100%). The removal of PAHs varied in the order: naphthalene ≈ acenaphthalene > anthracene ≈ pyrene > phenanthrene > fluoranthrene. The treatment combination having the maximum removal capacity was also used eficiently for the removal of PAHs from natural and fortified natural water. This article demonstrated adsorption-coagulation integrated system has the potential to remediate PAHs polluted water.

Effect of bentonite on heavy metal uptake by amaranth (Amaranthus blitum cv. Pusa Kirti) grown on metal contaminated soil

A pot culture experiment was conducted to assess the effect of bentonite application on heavy metal uptake by amaranth (Amaranthus blitum cv. Pusa Kirti). Amendment of soil with bentonite @ 2.5% significantly improved the plant growth by 76.5 and 41.7% in first and second harvest, respectively. The metal concentration of amaranth reduced by 6.5 & 21.2% for Zn, 30.5 & 29.9% for Cu and 34.4 & 40.2% for Ni at first and second harvest, respectively on application of 2.5% bentonite. Amending the soil with bentonite (2.5%) significantly decreased the bioconcentration factor (BCF) of metals by 74 and 28% for Zn, 38 and 36% for Cu, 44 and 34% for Ni at first and second harvest, respectively. The hazard quotient (HQ) for metal uptake through consumption of amaranth was significantly reduced by application of bentonite @ 2.5% as it immobilises heavy metals in polluted soil.