Scholarly article on topic 'Sustaining Irrigated Agriculture in Mediterranean Countries with Treated Municipal Wastewater: A Case Study'

Sustaining Irrigated Agriculture in Mediterranean Countries with Treated Municipal Wastewater: A Case Study Academic research paper on "Agriculture, forestry, and fisheries"

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{"Wastewater reuse" / "Water demand management" / "Non-potable water" / Disinfection / Filtration / "Membrane BioReactor."}

Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — P. Vergine, A. Lonigro, P. Rubino, A. Lopez, A. Pollice

Abstract Results of field experiments of wastewater reuse are presented. Fennel and lettuce were irrigated with four different water sources: three reclaimed wastewater streams, obtained by applying different treatment schemes to the same municipal wastewater, and a conventional source. Differences between the three effluents were significant in terms of suspended solids and faecal indicators. Both lettuce and fennel yields were enhanced by the high content of nutrients in the effluent of one of the treatment plants, which had been operated for partial nitrogen removal. Substituting chemical fertigation with the supplying of nutrients contained in the irrigation water enhanced fennel productivity.

Academic research paper on topic "Sustaining Irrigated Agriculture in Mediterranean Countries with Treated Municipal Wastewater: A Case Study"

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Procedía Engineering 89 (2014) 773 - 779

Procedía Engineering

www.elsevier.com/locate/procedia

16th Conference on Water Distribution System Analysis, WDSA 2014

Sustaining Irrigated Agriculture in Mediterranean Countries with Treated Municipal Wastewater: A Case Study

P. Verginea'*9 A. Lonigrob, P. Rubinob, A. Lopeza, A. Pollicea

aCNR IRSA, viale F. De Blasio 5, Bari 70132, Italy bDip. Scienze Agro-Ambienali e Territoriali, Universita di Bari, ViaAmendola,165/A- 70126 Bari, Italy

Abstract

Results of field experiments of wastewater reuse are presented. Fennel and lettuce were irrigated with four different water sources: three reclaimed wastewater streams, obtained by applying different treatment schemes to the same municipal wastewater, and a conventional source. Differences between the three effluents were significant in terms of suspended solids and faecal indicators. Both lettuce and fennel yields were enhanced by the high content of nutrients in the effluent of one of the treatment plants, which had been operated for partial nitrogen removal. Substituting chemical fertigation with the supplying of nutrients contained in the irrigation water enhanced fennel productivity.

© 2014PublishedbyElsevier Ltd.Thisis anopen access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of WDSA 2014

Keywords: Wastewater reuse; Water demand management; Non-potable water; Disinfection; Filtration; Membrane BioReactor.

1. Introduction

In order to mitigate water stress, treated municipal wastewater is one of the most readily available alternative water resources. Water demands in the Mediterranean area can be barely covered by the conventional resources exploitation and must partly use non-renewable resources or non-conventional supply sources [1].

Apulia (southern Italy) is one of the Mediterranean regions most heavily affected by water shortage, moreover its economy is strongly based on irrigated agriculture. Nevertheless in Apulia only 1% of treated wastewater potentially available for reuse in agriculture is presently used, mainly because of regulatory problems and public acceptance.

* Corresponding author. Tel: +390805820517; Fax: +390805313365. E-mail address: pompilio.vergine@ba.irsa.cnr.it

1877-7058 © 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Organizing Committee of WDSA 2014 doi: 10.1016/j .proeng.2014.11.506

Within a large nationally funded research project started in 2011 (whose acronym is In.Te.R.R.A.), several types of treatment schemes were applied at the pilot and full scale to treat municipal wastewater and polish secondary effluents for reuse in irrigation at the field scale. In the present study, results from one year of field tests carried out at one of the experimental sites are presented.

Nomenclature

BOD Biological Oxygen Demand

COD Chemical Oxygen Demand

EC Electrical Conductivity

E.coli Escherichia Coli

GDF Gravity Disk Filter

IFAS-MBR Integrated Fixed Activated Sludge Membrane BioReactor

SAR Sodium Absorption Ratio

TSS Total Suspended Solids

UV Ultraviolet

WWTP Wastewater Treatment Plant

2. Materials and Methods

2.1. Wastewater treatment plants

The reclaimed wastewater streams used to irrigate the experimental field were the effluent of the local full-scale municipal wastewater treatment plant (WWTP) and the effluents of two pilot plants installed at the WWTP facilities (PP1 and PP2). The three treatment plants are schematised in Fig. 1. The full-scale WWTP had a conventional scheme, whose tertiary treatments consisted of coagulation-flocculation, sand filtration and chlorination.

The first pilot plant (PP1) treated the raw municipal wastewater through a biological process, called IFAS-MBR (Integrated Fixed Activated Sludge Membrane BioReactor [2]), in which attached and suspended biomasses coexist. Solid/liquid separation was provided through submerged hollow fiber membranes operating out-in (GE Water) and with a nominal pore size of 0.1 ^m . UV radiation, performed in a closed vessel, was applied as final disinfection step and operated only during irrigation.

The second pilot plant (PP2) treated the secondary settled effluent of the full-scale WWTP by two processes: cloth filtration, operated continuously in a GDF (Gravity Disk Filter [3]), and UV radiation, performed in an open channel and operated only during irrigation. The GDF mostly works in a still mode and water treatment occurs by passive (gravity) filtration through the cloths. Polyester filters with 20 ^m mesh were used. The effluent of the GDF went continuously into the channel UV system, where lamps were automatically activated when the irrigation line was switched on.

2.2. Irrigation of crops

In a 2000 m2 experimental field two different crops, fennel and lettuce, were grown in succession. Four different water sources were used for the irrigation and compared adopting a randomized block design, constituted of 16 plots, as shown in Fig. 1. The reclaimed wastewater streams (WWTP, PP1 and PP2) were pumped directly from the treatment plants to the irrigation system serving the experimental field. The conventional water (control) was drinking water. Due to problems with the automatic pressure switch of the PP2 irrigation pump, during both growing seasons the PP2 plots were partially irrigated with control water. Therefore the related agronomic results were discarded.

PP2 Experimental field

©¿SM control

control

3-5m3/irrigation

control

municipal wastewater

Pilot Plant2 (PP2)

25m3/h j Gravity i 3-5m3/irrigation

"1 Disk Filter i....................

full scale Waste WateriTreatment Plant (WWTP)

primary activated secondary coagulation sand chlorination

settler sludge settler flocculation filtration

Pilot Plant 1 (PP1)

Integrated Fixed Activated I Sludge Membrane BioReactor

f . "i 3-5m3/irrigation

reservoir ■--------

Fig. 1. Layout of the experimental design, including the irrigation system and the wastewater treatment plants.

Lettuce was transplanted in single rows, 0.5 m apart from each other, realizing a theoretical plant density of 6.7 plants/m2. Fennel was transplanted in single rows, 0.5 m apart from each other, realizing a theoretical plant density of 10.0 plants/m2. For both crops, drip irrigation was adopted by placing the dripping lines between every other row.

Crops were irrigated when the soil water deficit in the root zone was equal to 35% of the total available water. Irrigation was scheduled based on the évapotranspiration criterion, providing water to the crops when the following conditions were met:

• kp ■ kc -Re ) = d (1)

where d is equal to 10 for lettuce and 16 for fennel, n is the number of days required to reach soil water deficit limits starting from the last watering, E is "class A" pan evaporation (mm), kc is the crop coefficient, kp is the pan coefficient (0.8) and Re is the rainfall (mm). The volumes of rainfall and irrigation are reported in Table 1, where also the amounts of nutrients supplied by chemical fertilization are shown.

In order to evaluate effects of irrigation with a water source containing a high concentration of nitrogen, the biological reactor of the PP1, i.e. the IFAS-MBR, was operated for partial nitrogen removal during both growing seasons. The content of nitrogen (mainly nitrates) in the PP1 effluent was used as additional nutrient source for lettuce cultivation, while it completely substituted fertigation for fennel cultivation.

Table 1. Crops cultivation data.

Crop Water source Transplanting Harvesting Basal dressing Fertigation Rainfall Irrigation volume

(dd/mm/yy) (dd/mm/yy) (KgP205/ha) (kgN/ha) (kgN/ha) (m3/ha) (m3/ha)

Lettuce control 18/04/13 25/06/13 100 39 80 320 1840

Lettuce WWTP 18/04/13 20/06/13 100 39 80 320 1660

Lettuce PP1 18/04/13 17/06/13 100 39 80 320 1500

Fennel control 31/08/13 14/01/14 100 40 110 2980 1080

Fennel WWTP 31/08/13 17/12/13 100 40 110 2720 1080

Fennel PP1 31/08/13 10/12/13 100 40 0 2720 1080

2.3. Analyses

Reclaimed water quality was monitored in terms of chemical and microbiological parameters and compared with conventional water. Microbiological indicators E.coli and Salmonella spp were measured at harvesting time in soil and on the edible parts of crops. Nitrates concentration and water content of the crops and the organic fraction of the soil were also measured. Analyses were performed according to standard methods [4, 5, 6].

3. Results

3.1. Reclaimed wastewater quality

Average values of the main parameters characterising the effluents of the three treatment plants are reported in Table 2. The effluent of the full scale WWTP complied with the local standards for reuse in agriculture, except for E. Coli.

Table 2: Characteristics of the effluents of the treatment plants (WWTP, PP1, PP2) are compared with the conventional water (control). Average values (and standard deviations) of the year 2013 are shown.

Parameter Control WWTP PP1 PP2 Local limits for reuse

EC (^S/cm) 1160±368 988±224 790±99 704±54 3000

PH(-) 7.2±0.2 7,7±0.1 7.1±0.5 7.2±0.2 6.0-9.5

COD (mg02/L) <15 20.6±3.8 20.8±5.3 27.8±9.0 100

BOD5 (mg02/L) 4.6±2.7 5.2±3.6 6.7±4.3 6.0±1.7 20

NH,+ (mgN/L) <1 <1 4.6±9.2 <1 2

N03-(mgN/L) 2.4±0.8 6.4±5.7 28.2±20.7 8.2±7.2 35(*)

Total Phosphorus (mg/L) 0±0 4.6±3.0 8.3±5.7 5.0±2.9 10

TSS (mg/L) <2 4.8±1.0 <2 13.5±9.5 10

Free Chlorine (mg/L) <0.2 <0.2 <0.2 <0.2 0.2

CI" (mg/L) 100±111 102±24 103±25 67±27 250

SAR (-) 0.9±0.8 1.1±0.1 0.8±0.1 1.1±0.1 10

Total Coliforms (CFU/100mL) 23±11 2074±1879 80±84 2027±1686 -

Faecal Coliforms (CFU /100mL) 2±3 1772±1707 20±14 917±1374 -

E.coli (CFU /100mL) 0±0 1462±1536 1±2 206±247 10<">

Salmonella spp Absent Absent Absent Absent Absent

Limit related to Total Nitrogen. (**' Limit that has to be respected by 80% of the samples (maximum value=100 CFU /lOOmL).

Considering that the IFAS-MBR was operated only for partial nitrogen removal, results suggest that the PP1 has the potential for producing water suitable for agricultural reuse (e.g. complying with local laws). E.coli in the effluent of the IFAS-MBR was never detected, but its concentration varied between 3 CFU/100mL and 142 CFU/100mL in the reservoirs where the effluent of the IFAS-MBR is accumulated, pointing out that: microbiological contamination or bacteria regrowth sometimes occurred in the tanks; the final disinfection step, operated by a closed vessel UV system, was effective, since E.coli in the effluent of the PP1 was below 10 CFU/100mL on average.

As for the PP2, results showed that the GDF allowed a consistent removal of TSS (and of the related COD), while it was ineffective for the treatment of nitrogen, phosphorus and microbiological contamination. TSS removal performances of the GDF resulted dependent on the influent characteristics. In particular, as shown in Fig. 2, a linear relationship between TSS in the influent and TSS in the outlet was observed in the range 0-50 mgTSS/L entering the filter. The solid content in the GDF effluent was often above 10 mgTSS/L. This caused an accumulation of solids in the UV channel (settling), which needed a periodical cleaning. As a consequence, the UV effectiveness varied between 1 and 4 log of E.coli abatement.

3.2. Effects on crops and soil

The effects of the water sources used for irrigation on crop yields and on the characteristics of vegetables and soil were evaluated. Data concerning the PP2 plots were not taken into account, because they have been partially irrigated with control water, due to problems with the irrigation pump automatic pressure switch.

As reported in Table 1, during lettuce cultivation all the plots received the same amount of chemical fertilizers, while during fennel cultivation the PP1 plots received only the basal dressing. The contribution of nutrients related to the irrigation water was very different between the three water sources (control, WWTP and PP1). In particular there were big differences in terms of nitrogen concentration, as can be seen from Table 2. In Fig. 3 the amount of nutrients supplied and the related yields obtained are represented for both the crops.

Results concerning lettuce cultivation show that the higher (more than double) amount of nutrients received by the PP1 plots, compared with control and WWTP plots, caused a significant higher crop production, even if lettuces cultivated in PP1 plots were harvested about one week in advance, as reported in Table 1. Considering this result, during fennel cultivation fertigation was not performed on the PP1 plots, which, due to the limited demand of irrigation during the rainy season, received also a small amount of nutrients from the irrigation water. As a consequence, the overall supplying of nitrogen on PP1 plots was smaller than on other plots. Nevertheless in PP1 plots fennel production was significantly higher, if compared with control plots, and, moreover, fennel were harvested about one month in advance, as reported in Table 1.

Considering all results concerning crop yields, it seems that both production and growth rate can be enhanced by increasing the overall amount of nutrients supplied or, as well, by increasing the frequency of nutrients supplying, as occurred for PP1 plots during fennel cultivation.

Concentration of nitrates and dry matter were measured in representative samples of fresh fennel and lettuce. No relevant differences in terms of nitrate concentration in the vegetables were noticed between the plots irrigated with different water sources. In all the cases NO3 concentration was clearly below the standard limits (from four to five times smaller). On the contrary, dry matter in crops irrigated with treated wastewater, either with PP1 or WWTP effluent, was slightly higher than in crops irrigated with conventional water.

No significant differences were noticed in terms of percentage of organic matter in the soil. Microbiological indicators E.coli and Salmonella spp were also measured in soil and edible parts at harvesting time. Salmonella spp was absent in all the samples. E.coli was never detected on fennel and in the corresponding samples of soil, irrespective of the irrigation water source. Regarding lettuce cultivation, E.coli concentration was always zero in samples related to PP1 and control plots, whereas, for plots irrigated with WWTP effluent, the average concentration of E.coli was 4 CFU/10g in the soil and 45 CFU/10g on the edible parts of lettuce. These results are similar, in terms of E.coli concentration in water, soil and vegetables, to those obtained by Holvoet et al. [7], which present results of a survey performed in Belgian farms that use a conventional water source (well water) for irrigation.

Fig. 2. Relationship between TSS in the influent and effluent of the Gravity Disk Filter.

■ crop yield B N from fertilization □ N from irrigation

0 P from fertilization □ P from irrigation

lettuce lettuce lettuce fennel fennel fennel control WWTP PP1 control WWTP PP1

Fig. 3. For every group of plots characterized by the same irrigation water source (WWTP, PP1, PP2), the amounts of nutrients supplied during the entire growing season and the resulting crop yields are displayed.

4. Conclusions

Comparing the performances of three treatment schemes, applied to the same municipal wastewater, significant differences were noticed in terms of suspended solids and faecal indicators removals. The pilot plant PP1, composed of an advanced biological reactor (IFAS-MBR) and an UV disinfection system, had the best performance for producing water suitable for agricultural reuse (e.g. complying with local laws).

The pilot plant PP2, constituted of Gravity Disk Filter and UV radiation, compared to the full-scale WWTP tertiary treatment (coagulation-flocculation, sand filtration and chlorination), achieved a higher E.coli abatement, but had worse performance in terms ofTSS removal.

Managing the biological process only for partial nitrogen removal allowed the supplying of a consistent fertilization contribution with the irrigation water. This had positive effects on yield and growth rate of both lettuce and fennel, without affecting the qualitative characteristics of the crops.

In particular results related to fennel cultivation showed that substituting chemical fertigation with the supplying of nutrients contained in the irrigation water enhanced crop productivity, even if the overall amount of nitrogen supplied was reduced.

Acknowledgements

This work has been financed by Italian government (MIUR) and European Commission (FESR). References

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