Use of natural mucilage extracted from the Stenocereus griseus (Cardón Guajiro) plant as a coagulant in the treatment of domestic wastewater

Tratamento primário de águas residuais domésticas a partir da mucilagem natural extraída da fábrica de Stenocereus griseus (Cardón Guajiro) como coagulante

Abstract

Coagulants can be extracted from vegetal material and applied in the treatment of wastewater. These coagulants are derived from seeds, leaves, bark, roots and fruits. This study focuses on the use of the mucilaginous extract ofStenocereus griseus(known as Cardón Guajiro) for removal of biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), total solids, turbidity and color in domestic wastewater from a pumping station in the city of Cartagena (Colombia). The optimal dose ofS. griseusextract was determined by a pitcher test employing an E&Q F6-300 digital flocculator. All physicochemical tests were carried out following the specifications of the standard methods for wastewater (APHA). When 1400 mgL^-1 of natural coagulants were used in the sewage treatment, the turbidity obtained was 29.57 TNU, representing removal of 67.24%, considering the initial turbidity. This parameter decreases until 68.61 PCU, for a 72.12% removal at the same coagulant dosage regarding the color. It must be noted that significant statistical differences were found between all tested doses of the coagulant. The mucilaginous extract of S. griseus exhibited useful properties in the primary treatment of domestic wastewater.

Keywords:
coagulation; color; removal; turbidity; water treatment

Resumo

Os coagulantes podem ser extraídos de matéria vegetal e aplicados no tratamento de efluentes. Esses coagulantes são derivados de sementes, folhas, cascas, raízes e frutos. Este estudo enfoca o uso do extrato mucilaginoso de Stenocereus griseus (conhecido como Cardón Guajiro) para a remoção da demanda bioquímica de oxigênio (DBO₅), demanda química de oxigênio (COD), sólidos totais, turbidez e cor em águas residuais domésticas de uma estação de bombeamento na cidade de Cartagena (Colômbia). A dose ideal de extrato de S. griseus foi determinada por um teste de jarro empregando um floculador digital E & Q F6-300. Todas as determinações físico-químicas foram realizadas seguindo as especificações dos métodos padrão para efluentes da APHA (Standard Methods for Water and Wastewater). Quando foram utilizados 1400 mgL^-1 de coagulante natural no tratamento de esgoto, a turbidez obtida foi de 29,57 TNU, representando remoção de 67,24% considerando a turbidez inicial. Este parâmetro diminui até 68,61 PCU para uma remoção de 72,12% na mesma dosagem de coagulante em relação à cor. Deve-se notar que diferenças estatísticas significativas foram encontradas entre todas as doses testadas do coagulante. O extrato mucilaginoso de S. griseus, teve propriedades valiosas no tratamento primário de águas residuais domésticas.

Palavras-chave:
coagulação; cor; remoção; tratamento de água; turbidez

1. INTRODUCTION

Domestic wastewater processes involve physicochemical treatment (coagulation and flocculation). Coagulation is defined as adding chemicals reagents to wastewater for agglutination of small particles into larger particles that can be removed by solids processes (Ang and Mohammad, 2020; Luo et al., 2020; Guzmán et al., 2013). A wide range of wastewater treatments has been developed over the last decades. These treatments can be classified into physical (sedimentation, filtration, adsorption and UV), chemical (coagulation, electrochemical, ion exchange, oxidation, catalytic reduction and disinfection) and biological (phytoremediation and biodegradation) (Kooijman et al., 2020; Ang and Mohammad, 2019; Hamzah et al., 2017; Kumar and Chowdhury, 2020; Hoong and Ismail, 2018).

Coagulation is an essential process for removing turbidity, color and organic matter in domestic and industrial wastewater. Some coagulants employed to remove impurities and colloidal particles from wastewater are ferric chlorides, aluminum sulfate, polyaluminum chloride, and calcium carbonate (Bergamasco et al., 2009). Nevertheless, there are some disadvantages related to the use of coagulants, such as cost, production of large volumes of sludge and pH modifications of the treated water (Olivero et al., 2014; Yin, 2010). Bergamasco et al., 2009). Several studies have reported the efficiency of some low-cost coagulants employed in wastewater treatments. For example, Jaafari et al. (2020) employed a magnetic chitosan to remove anionic dyes from polluted waters. Likewise, Naghipour et al. (2018) carried out studies to remove diclofenac from aqueous solutions using activated pine charcoal as adsorbent material.

Natural coagulants have been studied as an alternative to traditional chemical coagulants. Some natural coagulants studied are those obtained from vegetal species such as Moringa oleifera (Okuda et al., 1999; Caldera et al., 2007) from Cereus deficiens (commonly known as cactus or cardon lefaria) (Martínez et al., 2003) and from Opuntia cochinellifera (Almendárez de Quezada, 2004). The genus Stenocereus (Berger) Riccob Comprises a heterogeneous group of cacti distributed from southern Arizona to northern Colombia and Venezuela (Anderson, 2001; Terrazas et al., 2005). The "cardón guajiro" or "yosú" (in Wayúu language), Stenocereus griseus (Haw.) Buxb, is a columnar cactus that can reach up to 11 m in height. In Colombia, it is present in the departments of Guajira, Cesar and Magdalena. This vegetal species has not been studied previously as a coagulant of wastewater.

However, the active compounds of cardon guajiro, such as polysaccharides and proteins, can be a useful alternative to coagulation and flocculation processes of various pollutants. It is also a plant that grows easily on the north coast of Colombia; it has low cost and does not generate a negative environmental impact, which makes this plant a very attractive source of coagulant material for the industry. This work therefore focuses on evaluating the use of mucilage extracted fromStenocereus griseusas a natural coagulant in domestic wastewater.

2. MATERIALS AND METHODS

2.1. Wastewater sample

The wastewater was obtained from a pumping station located in Cartagena de Indias, Colombia. The water sample was collected in the morning because, at that time, there was maximum discharge volume and the wastewater presents high levels of turbidity. The plants ofS. griseuswere obtained from the northern region of Colombia, at San Juan del Cesar in Guajira.

2.2. Physicochemical characterization of wastewater.

The wastewater sample was characterized following the Standard Methods for Water and Wastewater (APHA et al., 2012). For color determination, a colorimeter (Lovibond PFX 195) was employed using the 2120B method; the results were expressed as platinum-cobalt units (PCU). Turbidity was determined by the nephelometric method (Method 2130B) using a turbidity meter (Turbiquant 3000 IR). The pH was assessed by potentiometry with a digital potentiometer (Bench pH/Conductivity meter PC 510). Alkalinity was calculated by titration (expressed in mg of CaCO₃/L). Hardness was measured by titration using an EDTA solution as the titrating agent; this parameter was expressed in mg of CaCO₃/L. Table 1 shows the values obtained for the wastewater characterization.

Table 1.
Physicochemical characterization of domestic wastewater.

Parameters	Value	Unit
Total alkalinity	218.0±1.00	mg CaCO3L-1
Biochemical Oxygen Demand (BOD5)	128.1±0.81	mgL-1
Chemical Oxygen Demand (COD)	219.4±0.76	mgL-1
Total hardness	490.0±0.57	mg CaCO3L-1
Conductivity	1210.2±0.8	µScm-1
Turbidity	90.28±1.00	NTU
Color	246.1±0.60	UPC
Total solids	610.0±0.22	mgL-1

2.3. Preparation of the coagulant

The mucilage (coagulant) was extracted from plants of S. griseus, especially the section between the bark and the woody tubular medulla (stem pulp). The epidermis was removed from fragments of S. griseus stems and the parenchymatous tissue. This parenchyma was liquefied for one (1) minute. Then, the solid phase was separated from the aqueous phase and the aqueous phase mass was determined by gravimetry. Finally, distilled water was added to obtain a mucilaginous heterogeneous mixture (Fuentes et al., 2011).

2.4. Coagulation process

The standard jar test described by Satterfield (2005) was used to determine the optimum coagulant dosage. The mucilaginous mixture described in Section 2.3 500 mL of coagulant-wastewater solutions at different concentrations (800, 1000, 1200, 1400 and 1600 mg L^-1) was prepared employing wastewater without coagulant and another containing Al₂(SO₄)₃ as control. Then, both wastewaters (with and without coagulant) were subjected to agitation at 100 rpm during 1 minute, followed by slow agitation at 40 rpm for 30 minutes. Finally, all samples were left for 60 minutes to allow sedimentation (Tarón et al., 2017). The assays were performed at room temperature in an E&Q F6-300 Digital Flocculator.

The turbidity removal percentage was determined using Equation 1.

$Turbidityremoval\left(\%\right)=\frac{T_0-T_f}{T_0}*100$ (1)

Where: T _o is the initial value of turbidity and y T _f is the final value of turbidity.

The percentage of color removal was determined using Equation 2.

$colorremoval\left(\%\right)=\frac{Co-Cf}{Co}*100$ (2)

Where, C _o is the initial value of color and C _f is the final value of color.

2.5. Statistical analysis

The results were analyzed by means of ANOVA (one way) to determine statistically significant differences (P<0.05) among the samples. The software SPSS (Version 17.0 for Windows) was used. All tests were done in triplicate.

3. RESULTS AND DISCUSSION

3.1. Physicochemical characterization of the effluent after treatment with coagulants

Table 2 shows the physicochemical parameters evaluated in wastewater subjected to coagulant at different dosages. Statistical differences can be seen (P<0.05) between initial and final values of alkalinity at doses 800, 100 and 1200 mgL^-1 of the mucilaginous extract ofS. griseus(MES. g). These removal percentages are lower than those found for (Al2(SO4)3 at all doses tested. At 1400, 1600 and 1800 mgL-1 of MES. g,no significant differences (P>0.05) were found. The results are similar to those reported by Dearmas Duarte and Ramírez Hernández (2015), that achieve efficient nutrient removal through the use of natural and chemical coagulants in a wastewater treatment plant.

As doses of MES. g increase, the percentages of total solids removed also increase. The highest percentage of removal was 70.49%, which was reached employing a coagulant dosage of 1400 mgL^-1. When high doses (>1600mgL^-1) of coagulant were used, a slight increase in solid content was observed due to the load that can produce a re-stabilization of the system. This behavior also could be associated with the increase of coagulant requirement when the suspended solids rise, since the polymers can present an optimum coagulant concentration that depends on the molecular weight and ion concentration solids in suspension (Sánchez and Untiveros, 2004).

Regarding the chemical coagulant employed (Al₂(SO₄)_3, a similar behavior was seen. However, it must be noted that solids-removal levels are higher using low doses of coagulant (25 mgL^-1). The highest percentage of solid removal was 74.95; this is in accordance with the observations of Dearmas Duarte and Ramírez Hernández (2015). Statistical differences were appreciated among the percentages of solids removal using different dosages of coagulant. Presently, no investigations have been conducted pertaining to the use of coagulants extracted fromS. griseusfor water purification. Nevertheless, the effect of various suspensions ofStenocereus griseus,Cereus deficiens,Opuntia ficus-indicaand polyacrylamide on physical properties of the soil of Quibor (Lara State, Venezuela) has been evaluated, with Stenocereus griseus being considered the best flocculants (Henríquez et al., 2000).

The findings seen in Table 2 demonstrate that mucilaginous extract ofS. griseuscan be employed to decrease levels of biological and chemical degradation of organic matter. A higher percentage of chemical degradation of organic matter was reached when 1400 mgL^-1 of dosage of coagulant was used in the process. Statistical differences were observed among all coagulant dosages. Similar behavior was found for BOD₅; the best degradation result is obtained when high doses of coagulant (>1400 mgL^-1) are used. Statistical differences were noted between all values of BOD₅ obtained, as can be seen in Figure 1.

Table 2.
Physicochemical characterization of domestic wastewater using different dosages of coagulants.

Parametros	Dosages of mucilaginous extract ofS. griseus [mgL-1]
	Ci	800	1000	1200	1400	1600	1800	Unidades
Total alkalinity	218.0±1.0a	222±05b	230±2c	237±2d	240±1d	241±09d	242±2d	mg CaCO3 L-1
BOD5	128.1±0.81a	114±02b	102.1±08c	96.8±01d	57.64±1e	59.8±08e	60.6±01e	mgL-1
COD	219.4±0.76a	137±07b	104.7±04c	100±09d	70.5±03e	82.6±1.5f	84.2±1.3f	mgL-1
Total hardness	490.0±2.5a	450±2.1b	445±1.1c	409±1.5d	400±1.0e	402±1.9e	406±1.8d	mg CaCO3 L-1
Conductivity	1210.2±1.3a	1220±1ab	1226±1.2b	1252±3c	1250±4c	1251±2c	1260±3.1d	µScm-1
Turbidity	90.28±1.00a	54.7±05b	46.66±02c	33.8±01d	29.57±05e	32.4±02e	35.90±09f	NTU
Color	246.1±1.1a	180±1b	115.2±2c	80.50±2d	68.61±09f	70.6±05f	72.30±1g	UPC
Total solids	610.0±1.5a	335±08b	261.2±01c	219.±02d	180.4±08e	204±0.3f	211,1±07f	mgL-1
Dosages of Al2(SO4)3 [mgL-1]
	Ci	10	15	20	25	30	35
Total alkalinity	218.0±1.0a	219±02a	226±1.2b	230±2.3c	233±1.1c	239±2.2d	240±1.9d	mg CaCO3 L-1
BOD5	128.1±0.81a	105±0.8b	91.2±1.2c	82.9±1.6d	44.30±05e	47.8±1.1f	50.05±0.9f	mgL-1
COD	219.4±0.76a	123±2b	96.5±1c	82.4±09d	60.27±03e	68.4±09f	70.9±1.3f	mgL-1
Total hardness	490.0±2.5a	431±2.5b	430±1.5b	394±1.1c	381±2.1d	383±1.9d	389±1.2e	mg CaCO3 L-1
Conductivity	1210.2±1.3a	1213±4a	1220±2.3c	1239±2d	1248±3.1c	1252±1c	1256±2.5c	µScm-1
Turbidity	90.28±1.0a	42.4±09b	37.26±1c	28.7±09d	25.67±1.2e	26.9±1ed	27.5±1.1d	NTU
Color	246.1±1.1a	150±1.3b	100.5±2.2c	62.4±1.8d	51.11±1-4f	55.4±09g	59.90±1.6h	UPC
Total solids	610.0±1.5a	290±2.1b	246.1±2.2c	201.±1.9d	152.8±1.3e	180±1.6f	183.4±1.9f	mgL-1

• *rows with different letters are significantly different (p < 0.05); mean ± standard deviation of 3 repetitions.

Figure 1.
Removal of BOD₅, COD and total solids employing mucilaginous extract of S. griseus and the chemical coagulant Al₂(SO₄)₃. *Dosages of Al₂(SO₄)₃: 10, 15, 20, 25, 30 and 35 mgL^-1.

It is observed that Al₂(SO₄)₃ had better results than MES. g. with respect to the removal of COD and BOD₅. When 25 mgL^-1 of coagulant was used in the treatment, a BOD₅ removal of 65.41% was reached. However, it must be highlighted that the percentage of BOD₅ removal decreased at higher dosages, likely due to system restabilization. Regarding chemical oxygen demand, a similar behavior was obtained. Its mean, the highest removal percentage was 67.86, which was significantly different from the other values obtained with various coagulants. These findings are similar to those reported by Dearmas Duarte and Ramírez Hernández (2015), who reduced wastewater BOD to 62.63%.

As shown in Figure 1, chemical coagulant Al₂(SO₄)₃ presents better coagulation properties than natural coagulant (MES. g). It can be concluded that MES. gcould be an effective alternative to decrease BOD₅ and COD values in domestic wastewater treatment; these results corroborate the studies of Tarón et al. (2017) and Guzmán et al. (2013). It is important to mention that both industrial and domestic wastewater have key characteristics regarding the composition and structure of organic matter. Hence, a better understanding of organic matter's characteristics is important to improve treatment (Liu et al., 2016).

Color and turbidity are descending functions of MES. g concentration; the highest values of color and turbidity were 72.12 and 67.24%, respectively. These values were obtained using a coagulant concentration of 1400 mgL^-1. Similar findings were published by Dearmas Duarte and Ramírez Hernández (2015). At low doses of natural coagulant, the removal of color and turbidity was not significant, possibly due to the slowness of the coagulation process, a product of the low doses (MES. g). On the contrary, the use of high doses of MES. gis not adequate, since the system restabilizes and presents a stationary behavior, where there is little variation in color and turbidity removal.

In the case of Al₂(SO₄)₃, the higher removal percentage was obtained for both turbidity (71.56%) and color (79.23%); these values were obtained using a concentration of 25 mgL^-1 of Al₂(SO₄)₃. Comparing the turbidity removal percentages, significant statistical differences at p<0.05 between the two coagulants studied were observed. These results of BOD and COD are lower than those published by Tarón et al. (2017) in aqueous extract of Cassia fistula seed in the primary treatment of domestic wastewater (Figure 2).

Figure 2.
Turbidity and color removal using mucilaginous extract of S. griseus (MES. g) and Al₂(SO₄)₃. *Dosages of Al₂(SO₄)₃: 10,15,20,25,30 y 35 mgL^-1.

Although the coagulation mechanism of mucilage ofS. griseusin wastewater is unknown, it is presumed that pectins (mucilage) act as coagulant-flocculants. Mucilage is a polymer with high molecular weight, which can remain long and flexible, adsorbing various particles (Sánchez and Untiveros, 2004). Likewise, Gardiner et al. (1999) indicate no clear hypothesis for the mechanism of action of cactus extracts. However, these authors suggest that the mucilage synthesized are polysaccharides structured with functional groups such as -NH2, -COOH and -OH, which leave charges that promote hydrogen bond formation.

4. CONCLUSIONS

The mucilaginous extract ofS. griseus(MES. g) can be used as a coagulant in domestic wastewater treatment due to its properties to remove color, turbidity, BOD₅, COD and total solids. These properties are similar to some coagulants employed in primary treatment of domestic wastewater. The percentages of removal of both turbidity and color are promising and the dosages of inorganic chemical coagulants could be reduced. The highest removal percentages (70.42% for total solids, 72.12% color, 67.24% turbidity, 55% BOD5, and 67.86% COD) were obtained using a dosage of 1400 mgL^-1 of coagulant. These findings therefore could have interesting implications in the industry for the reduction of effluent contaminants.

5. ACKNOWLEDGMENT

The authors are especially grateful to the University of Cartagena for all their collaboration during the development of the research.

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Publication Dates

• Publication in this collection
  25 June 2021
• Date of issue
  2021

History

• Received
  04 Feb 2021
• Accepted
  03 May 2021