Exploring the efficacy of powered guar gum (Cyamopsis tetragonoloba) seeds, duckweed (Spirodela polyrhiza), and Indian plum (Ziziphus mauritiana) leaves in urban wastewater treatment

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Highlights

  • COD reduction in wastewater (WW) was in a good range (73.2–79.08%).

  • The WW nutrients (N–NO3 , PO4−3, and SO4−2) showed significant reduction (67.1–93.4%).

  • The 3 ml/L dose showed the optimal removal of WW pollutants.

Abstract

The efficiency of aqueous extract of powdered guar gum seed (Cyamopsis tetragonoloba), duckweed fronds (Spirodela polyrhiza), and Indian plum leaves (Ziziphus mauritiana) was tested to remove nitrate, sulphate, phosphate, and chemical oxygen demand from urban wastewater in this study. Coagulants were applied in four different doses (1, 2, 3, and 5 mL/L) without adjusting the pH of it in wastewater treatment and changes in wastewater parameters were measured. The crude extract of guar gum seed, Indian plum leaves, and duckweed exhibited the removal activities 71.7–95.03% (nitrate), 78.3–95.9% (phosphate), and 83.1–99.6% (sulphate). Nitrate removal was highest (93.5%), followed by phosphate (83.4%) and sulphate (77.7%). The 3 mL/L dose of coagulant showed the best results of wastewater treatment, followed by 2 mL/L, 1 mL/L, and 5 mL/L. Chemical oxygen demand reduction was also in a good range (73.2–79.08%) with 3 mL/L dose for all studied coagulants. pH reduced significantly in all setups of wastewater spiked with plant coagulants. The chemical analysis of Fourier transforms infrared (FTIR) spectroscopy of aqueous extract and plant powder indicates the presence of functions groups like – OH, –COOH, –NH, Cdouble bondO, C–C R–CHO, Cdouble bondC–CO–OH, C–H, and R–NH2, in raw coagulants. Overall, results indicate the possible utility of guar gum seed, duckweed, and Indian plum leaf powder as low-cost natural materials for treatment of urban wastewater. However, few high doses of coagulants showed a slight increase in chemical oxygen demand in wastewater, which can be moderated by purifying the active compounds responsible for coagulation activities.

Introduction

Coagulation and flocculation is a physicochemical process to treat water and wastewater for turbidity removal, which is mainly contributed by the organic colloidal materials and suspended particles. Many chemical-based coagulants/flocculants are widely used in conventional water treatment processes these include alum (AlCl3), ferric salts (FeCl3) and other synthetic organic polymers like polyacrylamide derivatives and polyethene amine (Sciban et al., 2009; Antov et al., 2010). Although, these materials are cheap and effective in the treatment of water and wastewater but not safe because of their residual impact on water quality, non-biodegradable nature and some toxicological impact on aquatic fauna. Mallevialle et al. (1984) revealed that residual monomers of some of these chemical coagulants cause neurotoxicity and have strong carcinogenic property also. One of the possible alternatives of these chemical-based coagulants could be the plant origin coagulants.

Nowadays, there is a growing concern on uses of natural coagulants derived mainly from plants, microorganisms and animals (Sciban et al., 2009). Some of the plant-based coagulants have properties like polymer bridging, charge neutralization, and double-layer compression (Amran et al., 2018), which could bind nutrients and other organic pollutants from water and wastewater on their surface and reduced in produced sludge. The natural coagulants are considered biodegradable and non-toxic and could cause the least impact on the chemical quality of water. Such coagulants also produce less quantity of sludge, which otherwise poses serious problems of handling and further disposal/treatment. In the recent past, several plant-based coagulants have been tested for turbidity removal from water and wastewater (Antov et al., 2010; Sciban et al., 2009).

Some of the plant parts (leaves, beans, seeds, and stems) contain a high amount starch, other carbohydrates, tannin and crude protein, which could be used as a natural coagulant for removal of various types of water and wastewater pollutants. Despite commercial plants, few plant weeds and wild plant species could serve the purpose of preparing green coagulants for wastewater treatment to avoid the utility of edible food resources for such operation. The literature review suggested the possible use of bean Phaseolus vulgaris (Antov et al., 2010), chestnut and acorn (Sciban et al., 2009), common Oak Quercus robur (Antov et al., 2018), Cactus latifaria and Prosopis juliflora (Diaz et al., 1999), Jatropha curcas and Carica papaya seed (Abidin et al., 2013; Kakoi et al., 2016), corn starch (Liu et al., 2017), in the removal of turbidity from water and wastewater. Few of the wild plants, which are available abundantly in tropical parts of the world are not tested for their coagulation-flocculation properties by any previous researcher. Duckweed is a common macrophyte available in Indian surface water bodies and has been tested for their efficacy in phytoremediation-based wastewater treatment and biomass yield as extra benefits for biomass energy generation (Verma and Suthar, 2014; Gusain and Suthar, 2017). A study by Utsev et al. (2017) revealed the suitability of duckweed Lemna trisulca based coagulant in the treatment of drinking water. They reported about 82–90% removal of turbidity when duckweed was allied in powder and filtrate from. However, the leaves of Indian plum (Ziziphus mauritiana) shrub contain substances like soluble carbohydrates, mucilage and some crude protein (Paul, 2006) that can be used for the preparation of coagulants. Guar (Cyamopsis tetragonoloba) is a dicot plant and its part (seed and whole bean) contain crude proteins in a considerable amount, which seems ideal for preparation of crude extracts for water treatment. Omer et al. (2013) have studied the efficiency of guar gum powder coagulant mixed with alum (1:1 ratio) in the removal of turbidity from drinking water. They found about 98–99.9% removal of turbidity from freshwater when applied with 120 mg/L alum solutions. In another study by Saritha and Sharmilaa (2013) have also reported significant removal (97%) of the organic load from tannery effluent (measured in chemical oxygen demand) when guar gum coagulant was applied with alum and polyaluminium chloride (PACl) in combinations. They found that guar gum (500–1000 mg/L) with PACl (100 mg/L) showed the best results in terms of COD reduction from the tannery effluent. Recent reports on the use of non-food plant materials in turbidity removal of fresh and artificial turbid water are described in Table 1. It is clear from the literature that in the majority of cases the plant-based materials are used for freshwater turbidity removal and treatment of sewage water using plant-based raw coagulant is rarely investigated by any previous researcher.

As per the authors best knowledge, no comprehensive report on the utility of duckweed (whole plant biomass), Indian plum leaves, and guar seed in sewage or urban wastewater is available in current literature. Most of the previous studies on guar gum have been conducted in combination with conventional chemical coagulants. This study aimed to investigate the possible uses of a few plant-based coagulants in the treatment of urban wastewater under lab-scale trials without adding any chemical substance. The outcome of this study would help design the low-cost processes for removal of nutrients from treated and untreated sewage water in wastewater treatment plants. In rural areas where water treatment and wastewater disposal is a major issue, such low-cost coagulants could help in treating the water for further community uses. The effect of coagulant dose on wastewater pollutant (N–NO3 , SO4−2, PO4−3, and COD) removal rate was also investigated in this study.

Section snippets

Plant material collection and processing

For this study, a total of three plant materials: duckweed (Spirodela polyrhiza) whole plant biomass, Indian plum (Ziziphus mauritiana), and guar seed (Cyamopsis tetragonoloba) were used for preparing the coagulant. Duckweed and Indian plum is very common in local areas as available in the wild and has no direct economic values. Duckweed poses a serious threat to aquatic life and can be used as a resource to address other environmental issues to solve two problems simultaneously weed management

Physicochemical characteristics of coagulants

The chemical characteristics of coagulants prepared from guar gum seed powder, Indian plum leaves, and duckweed fronds are described in Table 2. The pH of coagulant varied from 5.3 to 7.04 indicating slightly acidic to neutral while the turbidity was in the ranges of 6.89–7.22 NTU. The plant-based coagulants have shown effective coagulation activities with pH in the ranges of 7–10 (Yin, 2010), but the role of solution pH in coagulation activity is presumed complicated and more difficult due to

Conclusions

The aqueous extract of guar gum seed, duckweed fronds, and Indian plum leaves showed significant removal of wastewater pollutants. The following conclusion can be made from this study:

  • 1.

    The plant-based coagulants showed significant removal of NO3 (90–95.9%), PO4−3 (72.3–99.6%), and SO4−2 (71.1–83.1%) from urban WW.

  • 2.

    The total removal of WW nutrients was prominent in the duckweed-based coagulant followed by, guar gum seed and Indian plum leaves.

  • 3.

    The coagulant dose 3 mL/L was most effective in WW

CRediT authorship contribution statement

Neha Pandey: Data curation, Formal analysis, Methodology. Rita Gusain: Software, Visualization, Writing - original draft. Surindra Suthar: Conceptualization, Supervision, Validation, Writing - review & editing.

Declaration of competing interest

The authors declare that we have no conflict of interest with any individual and any organization.

Acknowledgement

The authors are grateful to Dr Sharifah R Wan Alwi, Associate editor, and Prof. Jiri Klemes, editor-in-chief for their kind editorial handling and supportive behaviour. The authors would like to thanks six anonymous reviewers for valuable suggestions and constructive comments on the earlier version of the manuscript.

References (45)

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