Purification of sewage wastewater though sand column filter for lessening of heavy metals accumulation in lettuce, carrot and cauliflower

doi:10.21203/rs.3.rs-1971096/v1

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Purification of sewage wastewater though sand column filter for lessening of heavy metals accumulation in lettuce, carrot and cauliflower

https://doi.org/10.21203/rs.3.rs-1971096/v1

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Sewage wastewater is rich in mineral nutrients contributed in plant growth and yield. However, accumulation of heavy metals in edible part of vegetables and fruits is dangerous for human health. Current research was conducted with aim to evaluate the performance of sand column filter for removal of heavy metals from sewage wastewater applied to the selected vegetables. Heavy metals content i.e. Pb, Ni, Cu and Fe were estimated higher in untreated sewage wastewater as compared to treated water. Number of leaves, fresh and dry weights of leaves, roots and total biomass of lettuce, carrot and cauliflower were improved due to irrigation of unfiltered sewage wastewater as compared to sewage wastewater. Curd diameter, fresh and dry weights of curd, and stem fresh weight of cauliflower, root length and diameter of carrot enhanced because of unfiltered sewage wastewater than treated sewage wastewater. The accumulation of heavy metals i.e. Pb, Ni, Cu and Fe was higher in roots, leaves and edible parts of the selected vegetables. In the present study, Cd and Cr concentrations were not affected from filtration process through sand column filter. Conclusively, filtration through sand column filter is very effective for removal of heavy metals from sewage wastewater to irrigate agricultural lands.

Growth and yield

Heavy metal concentration

Plant biomass

Reclamation of sewage wastewater

Freshwater is a unique resource with imperative qualities. Clean water is going to be reduced because of increased demand nearly three folds in South Asia, Africa and Middle East countries since 1950s (Gleick 2003). Poor distribution of irrigation systems, ground water with salty nature, low rainfall and rapid growth of population are major causes of water deficit conditions. This situation is leading towards untreated city wastewater usage for irrigation drives of agricultural lands. Application of sewage wastewater is becoming more popular run-through in developing world (Nath et al. 2009) especially in peri-urban areas of Pakistan (Khalil and Kakar 2011).

Wastewater is rich in organic and inorganic nutrient elements required for growth of plants (Khan et al. 2013). Farmers are frequently applying wastewater for their farming purposes in those areas located around the industrial zones and cities vicinity. Farmers considered that this is inexpensive and valuable source of minerals nutrients. Hence, farmers considered it as suitable alternative of fertilizers for plants growth (Murtaza et al. 2010). Macronutrients i.e. N, P and K, micronutrients i.e. Fe, Cu and Zn and considerable amount of organic matter are vital nutrients present in sewage wastewater contributed in plant growth and production (Gosh et al. 2012). The presence of macro and micronutrients in sewage wastewater enhanced growth and yield in corn (Harati 2003) and mulberry (Gul et al. 2021). Similarly, in another study, increased growth and yield was also recorded in chilli (Chalkoo et al. 2013), tomato and melon (Segura et al. 2002).

Heavy metals induced conditions in the soils are mainly due to sewage wastewater irrigation (Ullah et al. 2011). Excessive heavy metals deposition in agricultural lands resulted elevation of heavy metals accumulation in different plant parts. Hence, heavy metals accumulation is serious threat to food safety (Muchuweti et al. 2006). The recommended safe concentration of heavy metals for humans uptake is Fe (150 mg kg^-1), Pb (2 mg kg^-1), Cu (10 mg kg^-1), Ni (10 mg kg^-1), Cd (0.02 mg kg^-1) and Cr (1.3 mg kg^-1) (WHO, 1996). The consumption of contaminated fruits and vegetables from heavy metals is a serious danger for healthy life (Banerjee et al. 2011). These metals are very toxic and non- biodegradable even their ingestion is at parts per billion level causing numerous diseases (Singh et al. 2010). Heavy metals cause harmful impacts i.e. carcinogenic, teratogenic, neurotoxic, incurable and mutagenic concerns (Patra et al. 2010). The induced heavy metals conditions showed adverse effects on blood acidity, kidney damage, cancer, retardation (Gul et al. 2021). These situations might be shocking for vegetarians because their main food component is fresh vegetables.

Pakistan is one of the largest agricultural country. Its irrigation system mainly based on canal water of Indus Basin (Gul et al. 2021). Canal water is not sufficient to fulfill country farmers’ requirement for farming purposes due to increased population and different environmental fluctuations. Irrigation with sewage wastewater is very common practice in Pakistan. However, no serious actions have been taken to eradicate these dangerous concerns. Different management practices i.e. slow sand filter (Utami et al. 2012), thick tire chips (Abedi-Koupai et al. 2012), rubber chips (Bali and Tlili 2019) and and fine medial filters (Hatt et al. 2008) were used for elimination of heavy metals from sewage wastewater around the world.

For reduction of heavy metals, use of sand-based columns is firstly used in tomato and okra (Naz et al. 2021). However, sand-based columns are not used for lettuce, cauliflower and carrot. Therefore, present work was carried out to evaluate the capability of sand column for sewage wastewater filtration to lessen heavy metals and also evaluate the effects of unfiltered and filtered sewage waste water on growth, yield, and heavy metals buildup in leaves, roots and eatable parts of the selected vegetables.

Experimental details

Present research was carried out for evaluation of growth, yield and heavy metals in selected vegetables i.e. lettuce, carrot and cauliflower grown under filtered and unfiltered sewage wastewater for two years study (2014 & 2015) in the specific research site of Department of Horticulture, Bahauddin Zakariya University (BZU) Multan. Earthen pots were filled with 5 kg silt loam soil below corner to ensure easy watering. Main disposable of BZU campus was the source of sewage wastewater for treatments application.

Preparation of sand-based column

For sewage wastewater filtration, sand-based column contained mesh size sieves (0.5 mm). An iron sheet was placed inside and outlet was installed at the bottom. Column was filled with sand and sewage wastewater was passed through it. After that, filtered water was collected in container and sand was changed after one-time filtration for higher efficacy of the column. Afterward treatment application as filtered and unfiltered sewage wastewater was applied to the pots of the selected vegetables. Present research work was laid out under completely randomized design (CRD) under three repeats and each repeat comprised of ten pots. However, cultural practices for each crop were similar as their requirement.

Growth and yield traits

At the maturity stage, growth and yield of selected vegetables were collected from treated and untreated plants. Number of leaves were counted from each treatment. Fresh and dry weights of leaves, roots, plant biomass and curd were weighted using digital weighing balance. Curd diameter, root length and diameter were measured using Vernier caliper.

Determination of heavy metals

Chemicals preparation

For heavy metals extract, glassware was soaked for 12 hours in nitric acid solution of 10%. For estimation of standard value at 1000 mg L⁻¹, Ni, Cu, Cd, Pb, Fe, and Cr standards were bought from Merck and Co.

Pre-treatment of sewage wastewater before and after filtration

Water samples i.e. filtered and unfiltered collected from disposal unit were saved into airtight plastic bottles. According to a method of Singh (2013) approximately 5 mL of HNO₃ was poured into the plastic bottles to prevent from heavy metal reaction with plastic bottles during storage.

Digestion of plant samples for heavy metals extraction

Different plant parts i.e. roots, leaves and edible parts were harvested for determination of heavy metals from unfiltered sewage wastewater (control) and filtered sewage wastewater treated plants. Distilled water was used for washing plant parts and were dried by spreading on clean place for 60 mint. After that, plant parts were divided into small pieces and put in to the oven for drying till constant weight. Dried samples were finely ground and powder form was saved into zipper bags of polyethylene at ambient conditions for further downstream analysis. Approximately, grinded powder of 0.5 g from each treatment was subjected to acidic digestion 3: 1 contained 15 mL of HNO₃ and 5 mL of HClO₄. After that samples were placed on a hot plate at 80 °C. Heating remained continue until the appearance of colorless material. This material was collected in beakers for future downstream analyses as described method of Singh (2013).

Extraction of heavy metals from plant and water samples

Wet digestion method was used for extraction of heavy metals from water samples. After digestion of water and plant samples of selected vegetables, samples were filtered through Whatman No. 42 filter paper. Filtered samples and 25 mL of distilled water homogenized and saved in plastic bottles. Earlier described method of (Singh, 2013) was used for extraction of heavy metals from collected samples and identified through atomic absorption spectroscopy as well as photometer.

Statistical analysis

The collected data were evaluated using Statistix 8.1 as described method of (Steel et al. 1997) under two way factorial deign i.e. years’ and sewage wastewater treatment. However, individual, and interaction of years and sewage wastewater treatment were found to be non-significant therefore has not been discussed in results section. Means of sewage wastewater treatment were separated using LSD at 5% of probability.

Sewage wastewater characteristics before and after filtration used in the experiment

Physio-chemical properties i.e. pH, EC, HCO₃, RSC, Ca + Mg, Sulfate, Na and Cl of sewage wastewater before and after filtration used in the experiment (Table 1).

Heavy metal contents in unfiltered and filtered sewage wastewater Samples

Unfiltered sewage wastewater revealed significantly higher heavy metal contents i.e. Pb, Ni, Cu, Cd, Fe and Cr as compared to filtered sewage wastewater (Table 2). According to *WHO/FAO, all the studied heavy metals were found to be high in unfiltered water, while lower heavy metals were recorded in filtered water. The significant reduction in heavy metal content were observed in filtered water than unfiltered sewage wastewater (Table 2).

Growth and yield of spinach, carrot and cauliflower

Leaves number, leaves, roots and total biomass of fresh and dry weights were significantly greater under unfiltered sewage wastewater treated plants, while these traits were significantly lower under filtered sewage wastewater treated plants of the selected vegetables i.e. spinach, carrot and cauliflower (Table 3). However, number of leaves, fresh and dry weights of leaves, roots and total biomass were not affected from years’ effect (Table 3). Fresh weight, dry weight, and diameter of curd, and stem fresh weight were found to be higher in unfiltered sewage wastewater treatment, while curd diameter, fresh and dry weights of curd, and stem fresh weight were found to be lower in filtered sewage wastewater treated plants of cauliflower (Table 4). Similarly, root length and diameter of carrot were longer in unfiltered sewage wastewater treated plants, while shorter root length and diameter were measured in those plants treated with filtered sewage wastewater (Table 4).

Heavy metals buildup in leaves

The concentration of the studied heavy metals were significantly greater in leaves of those plants treated with unfiltered sewage wastewater, while significantly lower concentration was recorded in filtered sewage wastewater during both years I & II study on spinach, carrot and cauliflower (Table 5). However, Cd and Cr were not affected in leaves of selected vegetables from unfiltered and filtered sewage wastewater treatments during both years’ study (Table 5).

Heavy metals concentrations in roots

The maximum heavy metals were recorded in roots of unfiltered sewage wastewater, while these were the minimum in filtered sewage wastewater (Table 6). Cd and Cr were non-significant regarding treated and untreated plants of selected vegetables (Table 6).

Heavy metals concentrations in curds of cauliflower

Heavy metals i.e. Pb, Ni, Cu and Fe showed higher concentration in edible portion curd of cauliflower plants irrigated with unfiltered sewage wastewater, while lower concentrations of these heavy metals were measured in cauliflower plants irrigated filtered sewage wastewater (Table 7). Cd and Cr were non-significant regarding treated and untreated plants of cauliflower with sewage wastewater during both year I & II (Table 7).

Sand based column filter showed excellent potential to decrease heavy metals concentration in sewage wastewater. In the present study, filtered sewage water through sand column filter had low heavy metals concentrations than unfiltered sewage wastewater. Hence, filtration of sewage wastewater is effective for reduction in concentration of heavy metals. Similarly, significant reduction in Cu, Ni, and Pb was reported in filtered sewage wastewater than unfiltered sewage wastewater (Ngugi et al. 2022). In another study, Tauqeer et al. (2022) estimated that sand filter had potential to reduce heavy metals and organic pollutants from sewage wastewater.

Number of leaves were found to be higher in selected vegetables irrigated with unfiltered sewage wastewater as compared to filtered sewage wastewater. This increase in number of leaves was due to presence of essential nutrients present in sewage wastewater (Ahmed et al. 2022). Present findings are in accordance to earlier work of Naz et al. (2019) because sewage wastewater without filtration process increased the number of leaves in okra and tomato. Fresh and dry wrights of root, leaves and total biomass of the selected vegetables were enhanced due to presence of macro and micronutrients in sewage wastewater. Similar increase in growth and yield traits was also noted by Iqbal et al. (2013) in bell peppers. Therefore, present findings are in agreement to earlier of Boamponsem et al. (2012) because irrigation with sewage waste increase fresh and dry weights of roots, leaves and total biomass of lettuce, carrot and cabbage.

Fresh and dried weights of leaves of lettuce are edible parts increased due to sewage waste water and similar increase in leaves related traits was recorded in earlier work of Şentürk et al. (2022) in the lettuce. The availability of nutrients in sewage wastewater improved the size and weight of carrot roots and curd of cauliflower in the present study. Excellent leaves of lettuce, roots of carrot and curds of cauliflower are edible and higher yield contributing traits. Higher yield in the studied vegetables was recorded in unfiltered sewage wastewater as compared to filtered sewage wastewater. The decrease in fruit yield of those plants treated with sewage wastewater is mainly due to reduction of minerals content during filtration process. Hence, present study in agreement to previous studies of Naz et al. (2021) and Abbasi et al. (2021) because they proved that filtered sewage wastewater had less minerals as compared to unfiltered sewage wastewater. Hence, sand column is found to be effective for removal of toxic organic pollutants and reduction in heavy metals concentration from sewage wastewater

In the present study, studied heavy metals concentrations were increased in plant leaves, roots and edible parts due to irrigation with unfiltered sewage wastewater. The consumption of contaminated vegetables is very dangerous for health. However, markedly reduction in heavy metals concentration was estimated in filtered sewage wastewater. Hence, it has been evaluated that sand column filter had capability to reduce heavy metal concentration in sewage wastewater. The buildup of the heavy metals were increased in eatable parts because of irrigation with sewage wastewater (Anjum et al. 2021). Hence, sand column filter had better potential to filter sewage wastewater for irrigation purposes of agricultural crops (Pedrero et al. 2020). In the present study, reclamation of sewage wastewater did not effected the Cd and Cr concentrations. Different plant researchers evaluated that filtered water had less heavy metal concentration as compared to unfiltered sewage wastewater (Reddy et al. 2014). Present findings are in line to earlier work of Naz et al. (2019) because they also evaluated that and column had better capability to reduce heavy metals in two vegetables okra as well as tomato. Similarly, Naz et al. (2016) also studied that heavy metals were found to be higher in spinach plants when irrigated with sewage wastewater. Saini et al. (2021) studied that sand is effective strategy for reduction of heavy metal concentration from sewage wastewater which spoiled the fresh produce. Moreover, Verma et al. (2017) also evaluated that sand filter methods are effective for elimination of heavy metals and organic pollutant from sewage water and make water fit to irrigate agricultural lands.

Fresh vegetables are need of healthy life. Freshwater is depleted due to climate change. Therefore, utilization of ecofriendly filtration methods are important to utilize contaminated water for irrigation purposes. From current results, it has been concluded that sand column filter had better potential to reduce heavy metals i.e. Pb, Ni, Cu, Fe, Cd and Cr from sewag water. Sand column filter is cheap, eco-friendly, non-chemical and easy to use for farmers’ to filter industrial effluents/wastewater.

Author contribution SN, SA and HS interpreted the data and was a major contributor in writing the manuscript. SN, STAH and BS performed the experiment and collected the data. SN, MAA, HMDM and RA designed the experiment and contributed to the manuscript writing. All authors read and approved the final manuscript."

Funding Higher Education Commission of Pakistan

Data availability The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate Not applicable.

Consent for publication Not applicable.

Competing interests The authors declare no competing interests.

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Table 1: Physio-chemical properties of sewage wastewater before and after filtration used in the experiment

Sewage wastewater	pH	EC (dSm^-1)	HCO₃	RSC	Ca + Mg (meq L^-1)	Sulfate (meq L^-1)	Na (meqL^-1)	Cl (meqL^-1)
Unfiltered	7.3	0.183	13	4.4	9.6	1.09	8.79	5.02
Filtered	7.5	0.391	10	3.5	7.5	0.79	6.91	4.5

Table 2: Heavy metal content (mg L^-1) in sewage wastewater before and after filtration used in the experiment

Sewage wastewater	Pb	Ni	Cu	Cd	Fe	Cr
Unfiltered	2.48a	1.96a	3.26a	1.26a	8.76a	0.46a
Filtered	1.71b	1.35b	2.58b	0.83b	6.30b	0.32b
*WHO/FAO	5.0	0.2	0.2	0.2	5.0	0.1

* = Permissible limits of heavy metals. Treatment means showed significant difference at P ≤ 0.05.

Table 3: Growth, yield and biomass of selected vegetables affected from unfiltered and filtered sewage wastewater

Sewage wastewater	Spinach			Cauliflower			Carrot
Sewage wastewater	Year I	Year II	*Mean*	Year I	Year II	*Mean*	Year I	Year II	*Mean*
Number of leaves per plant (g)
Unfiltered sewage wastewater	36.43a	37.36a	*36.90a*	30.66a	32.33a	*31.50a*	10.00a	9.33a	*9.66a*
Filtered sewage wastewater	29.76a	33.20a	*31.48b*	30.66a	27.00a	*28.83a*	6.97a	6.93a	*6.95b*
Mean	*33.10a*	*35.28a*		*30.66a*	*29.66a*		*8.48a*	*8.13a*
Fresh weight of leaves per plant (g)
Unfiltered sewage wastewater	179.34a	183.99a	*181.66a*	420.33a	439.33a	*429.83a*	56.86a	44.66a	*50.76a*
Filtered sewage wastewater	147.00a	164.72a	*155.86b*	409.17a	397.07a	*403.12b*	32.52a	34.33a	*33.43b*
Mean	*163.17a*	*174.35a*		*414.75a*	*418.20a*		*44.69a*	*39.50a*
Dry weight of leaves per plant (g)
Unfiltered sewage wastewater	14.55a	14.94a	*14.74a*	67.67a	70.73a	*69.20a*	6.20a	5.96a	*6.08a*
Filtered sewage wastewater	11.94a	13.39a	*12.66b*	65.87a	63.92a	*64.90a*	4.63a	4.86a	*4.75b*
Mean	*13.25a*	*14.16a*		*66.77a*	*67.33a*		*5.41a*	*5.41a*
Fresh weight of roots per plant (g)
Unfiltered sewage wastewater	4.30a	4.83a	*4.56a*	62.66a	62.50a	*62.58a*	101.93a	106.67a	*104.30a*
Filtered sewage wastewater	2.76a	2.33a	*2.55b*	54.00a	52.33a	*53.16b*	95.97a	100.67a	*98.32b*
Mean	*3.53a*	*3.58a*		*58.33a*	*57.41a*		*98.95a*	*103.67a*
Dry weight of roots per plant (g)
Unfiltered sewage wastewater	0.86a	0.96a	*0.91a*	16.23a	16.16a	*16.20a*	9.96a	10.50a	*10.23a*
Filtered sewage wastewater	0.55a	0.46a	*0.51b*	11.86a	12.40a	*12.13b*	9.03a	9.30a	*9.16b*
Mean	*0.70a*	*0.72a*		*14.05a*	*14.28a*		*9.50a*	*9.90a*
Biomass on fresh weight basis (g)
Unfiltered sewage wastewater	183.64a	188.82a	*186.23a*	1343.6a	1351.4a	*1347.5a*	158.80a	151.33a	*155.07a*
Filtered sewage wastewater	149.77a	167.05a	*158.41b*	1290.2a	1270.6a	*1280.4b*	128.49a	135.00a	*131.75b*
Mean	*166.71a*	*177.94a*		*1316.9a*	*1311.0a*		*143.65a*	*143.17a*
Biomass on dry weight basis (g)
Unfiltered sewage wastewater	15.41a	15.90a	*15.66a*	274.36a	279.08a	*276.72a*	16.16a	16.46a	*16.31a*
Filtered sewage wastewater	12.50a	13.85a	*13.17b*	264.84a	262.18a	*263.51b*	13.66a	14.16a	*13.91b*
Mean	*13.95a*	*14.88a*		*269.60a*	*270.63a*		*14.91a*	*15.31a*

Treatment and year’s mean with different letters show significant difference at P ≤ 0.05

Table 4: Curd diameter, fresh and dry weights and fresh stem weight of cauliflower and carrot affected from unfiltered and filtered sewage wastewater

Sewage wastewater	Cauliflower
Sewage wastewater	Year I	Year II	*Mean*
Curd diameter (cm)
Unfiltered sewage wastewater	36.02a	36.46a	*36.24a*
Filtered sewage wastewater	31.30a	31.63a	*31.46b*
Mean	*33.66a*	*34.05a*
Curd fresh weight (g)
Unfiltered sewage wastewater	750.57a	753.23a	*751.90a*
Filtered sewage wastewater	737.53a	739.53a	*738.53b*
Mean	*744.05a*	*746.38a*
Curd dry weight (g)
Unfiltered sewage wastewater	182.38a	183.82a	*183.10a*
Filtered sewage wastewater	178.63a	178.62a	*178.62b*
Mean	*180.51a*	*181.22a*
Fresh weight of stem (g)
Unfiltered sewage wastewater	110.00a	96.33a	*103.17a*
Filtered sewage wastewater	89.50a	81.67a	*85.58b*
Mean	*99.75a*	*89.00a*
	Carrot
Root length (cm)
Unfiltered sewage wastewater	26.53a	29.00a	*27.76a*
Filtered sewage wastewater	25.23a	22.00a	*23.61b*
Mean	*25.88a*	*25.50a*
Root diameter (cm)
Unfiltered sewage wastewater	12.41a	12.93a	*12.67a*
Filtered sewage wastewater	11.06a	10.11a	*10.59b*
Mean	*11.74a*	*11.52a*

Treatment and year’s mean with different letters show significant difference at P ≤ 0.05

Table 5: Effect of unfiltered and filtered sewage wastewater on heavy metal concentrations (mg kg^-1) in leaves of spinach, cauliflower and carrot

Sewage wastewater	Spinach leaves			Cauliflower leaves			Carrot leaves
Sewage wastewater	Year I	Year II	*Mean*	Year I	Year II	*Mean*	Year I	Year II	*Mean*
Pb content
Unfiltered sewage wastewater	4.466a	4.700a	*4.583a*	12.700a	12.867a	*12.783a*	6.400a	6.833a	*6.616a*
Filtered sewage wastewater	3.233a	3.800a	*3.516b*	9.400a	9.333a	*9.367b*	4.666a	4.833a	*4.750b*
Mean	*3.850a*	*4.250a*		*11.050a*	*11.100a*		*5.533a*	*5.833a*
Ni content
Unfiltered sewage wastewater	13.100a	13.300a	*13.200a*	13.667a	14.000a	*13.833a*	12.467a	13.100a	*12.783a*
Filtered sewage wastewater	10.767a	11.400a	*11.083b*	10.667a	10.867a	*10.767b*	9.867a	9.933a	*9.900b*
Mean	*11.933a*	*12.350a*		*12.167a*	*12.433a*		*11.167a*	*11.517a*
Cu content
Unfiltered sewage wastewater	13.800a	14.067a	*13.933a*	15.800a	15.633a	*15.717a*	11.200a	11.900a	*11.550a*
Filtered sewage wastewater	10.933a	11.200a	*11.067b*	12.633a	12.700a	*12.667b*	9.700a	9.867a	*9.783b*
Mean	*12.367a*	*12.633a*		*14.167a*	*14.217a*		*10.450a*	*10.883a*
Cd content
Unfiltered sewage wastewater	0.400a	0.533a	*0.466a*	0.433a	0.466a	*0.450a*	0.333a	0.466a	*0.400a*
Filtered sewage wastewater	0.090a	0.133a	*0.111a*	0.334a	0.334a	*0.333a*	0.250a	0.266a	*0.258a*
Mean	*0.245a*	*0.333a*		*0.383a*	*0.440a*		*0.291a*	*0.366a*
Fe content
Unfiltered sewage wastewater	294.70a	295.73a	*295.22a*	356.53a	360.03a	*358.28a*	181.00a	190.83a	*185.92a*
Filtered sewage wastewater	238.50a	246.87a	*242.68b*	314.30a	317.80a	*316.05b*	146.80a	149.77a	*148.28b*
Mean	*266.60a*	*271.30a*		*335.42a*	*338.92a*		*163.90a*	*170.30a*
Cr content
Unfiltered sewage wastewater	0.090 a	0.126a	*2.400a*	2.433a	2.433a	*2.350a*	0.633a	0.766a	*0.700a*
Filtered sewage wastewater	0.056a	0.103a	*1.350a*	2.233a	2.266a	*2.333a*	0.466a	0.566a	*0.516a*
Mean	*1.800a*	*1.950a*		*2.250a*	*2.433a*		*0.550a*	*0.666a*

Treatment and year’s mean with different letters show significant difference at P ≤ 0.05

Table 6: Effect of unfiltered and filtered sewage wastewater on heavy metal concentrations (mg kg^-1) in roots of spinach, cauliflower and carrot

Sewage wastewater	Spinach roots			Cauliflower roots			Carrot roots
Sewage wastewater	Year I	Year II	*Mean*	Year I	Year II	*Mean*	Year I	Year II	*Mean*
Pb content
Unfiltered sewage wastewater	3.100a	3.166a	*3.133a*	6.800a	6.766a	*6.783a*	8.600a	8.866a	*8.733a*
Filtered sewage wastewater	2.666a	2.800a	*2.733b*	4.100a	4.266a	*4.183b*	6.800a	7.166a	*6.983b*
Mean	*2.883a*	*2.983a*		*5.450a*	*5.516a*		*7.700a*	*8.016a*
Ni content
Unfiltered sewage wastewater	11.133a	12.200a	*11.667a*	12.033a	11.733a	*11.883a*	15.800a	16.067a	*15.933a*
Filtered sewage wastewater	9.660a	10.133a	*9.867b*	9.167a	9.367a	*9.267b*	13.633a	14.500a	*14.067b*
Mean	*10.367a*	*11.167a*		*10.600a*	*10.550a*		*14.717a*	*15.283a*
Cu content
Unfiltered sewage wastewater	13.033a	13.800a	*13.417a*	15.467a	15.633a	*15.550a*	12.800a	13.800a	*13.300a*
Filtered sewage wastewater	9.267a	9.400a	*9.333b*	10.600a	11.100a	*10.850b*	9.967a	10.300a	*10.133b*
Mean	*11.150a*	*11.600a*		*13.033a*	*13.367a*		*11.383a*	*12.050a*
Cd content
Unfiltered sewage wastewater	0.300a	0.400a	*0.350a*	0.163a	0.133a	*0.148a*	0.600a	1.2667a	*0.933a*
Filtered sewage wastewater	0.090a	0.166a	*0.128a*	0.056a	0.023a	*0.040a*	0.466a	0.633a	*0.550a*
Mean	*0.195a*	*0.283a*		*0.110a*	*0.078a*		*0.533a*	*0.950a*
Fe content
Unfiltered sewage wastewater	258.33a	261.40a	*259.87a*	259.27a	261.73a	*260.50a*	226.53a	231.30a	*228.92a*
Filtered sewage wastewater	224.50a	233.73a	*229.12b*	315.47a	219.23a	*217.35b*	196.20a	199.37a	*197.78b*
Mean	*241.42a*	*247.57a*		*237.37a*	*240.48a*		*211.37a*	*215.33a*
Cr content
Unfiltered sewage wastewater	2.000a	2.100a	*2.050a*	2.167a	2.166a	*2.166a*	1.200a	1.300a	*1.250a*
Filtered sewage wastewater	1.433a	1.700a	*1.566a*	1.400a	1.600a	*1.500a*	0.833a	0.900a	*0.866a*
Mean	*1.716a*	*1.900a*		*1.783a*	*1.883a*		*1.016a*	*1.100a*

Treatment and year’s mean with different letters show significant difference at P ≤ 0.05

Table 7: Effect of unfiltered and filtered sewage wastewater on heavy metal concentrations (mg kg^-1) in cauliflower curds

Sewage wastewater	Cauliflower curds
Sewage wastewater	Year I	Year II	*Mean*
Pb content
Unfiltered sewage wastewater	2.466a	2.800a	*3.466a*
Filtered sewage wastewater	3.233a	3.700a	*2.633b*
Mean	*2.850a*	*3.250a*
Ni content
Unfiltered sewage wastewater	11.500a	11.767a	*13.933a*
Filtered sewage wastewater	9.300a	9.733a	*11.067b*
Mean	*12.367a*	*12.633a*
Cu content
Unfiltered sewage wastewater	12.267a	11.867a	*12.067a*
Filtered sewage wastewater	9.033a	9.333a	*9.183b*
Mean	*10.650a*	*10.600a*
Cd content
Unfiltered sewage wastewater	0.060a	0.196a	*0.128a*
Filtered sewage wastewater	0.023a	0.030a	*0.027a*
Mean	*0.0417a*	*0.113a*
Fe content
Unfiltered sewage wastewater	172.83a	181.60a	*177.22a*
Filtered sewage wastewater	136.20a	138.43a	*137.32b*
Mean	*154.52a*	*160.02a*
Cr content
Unfiltered sewage wastewater	1.500a	1.833a	*1.666a*
Filtered sewage wastewater	0.800a	1.100a	*0.950a*
Mean	*1.150a*	*1.466a*

Treatment and year’s mean with different letters show significant difference at P ≤ 0.05

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Purification of sewage wastewater though sand column filter for lessening of heavy metals accumulation in lettuce, carrot and cauliflower

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Abstract

Introduction

Materials And Methods

Results

Discussion

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