Effect of Treated Domestic Wastewater as Source of Irrigation Water and Nutrients on Rice Performance in Morogoro, Tanzania

JEWM

Effect of treated domestic wastewater as source of irrigation water and nutrients on rice performance in Morogoro, Tanzania

Agnes MS Nyomora Department of Botany, University of Daressalaam, P.O. Box 35060, Tanzania. Tel.: +255 222 410,764/255754478021; Email: agnesnyomora@gmail.com;nyomora@amu.udsm.ac.tz

A study was conducted in Morogoro, Tanzania to assess the effect of treated wastewater as an alternative source of irrigation water and nutrients for rice. Wastewater was sourced from a local wastewater Stabilization Ponds and cleaned through a Constructed Wetland. Four treatments namely, (i) Waste water (WW) only (ii) WW + NPK (iii) Tap water only (iv) Tap water + NPK were tested in a Randomized Complete Block Design (RCBD) with 4 replicates. Rice, variety Saro 5 was planted in August 2013.Data was collected on physical-chemical and biological qualities of the WW, and soils, yield and yield components. Analysis of variance and Least Significant Difference (LSD) on yield were conducted (p≤0.05) using INSTAT software. WW had alkaline pH of 8.2 and acceptable levels of physical-chemical-biological components. WW only treated rice resulted in higher yields over non-treated rice. The combination of WW and NPK was not as effective especially for flowering, grain size and total yield indicative of nutrients overloading. Tap water only treated rice yielded 1.3 tons/ha while WW treated rice yielded 5.44 ton/ha mostly through promotion of higher number of fertile tillers while a combination of WW and NPK depressed yield potential to only 1.7 ton/ha. Effectiveness of WW for irrigation is acknowledged.

Keywords: Constructed wetlands, saro 5 rice, irrigated rice, organic fertilizer, alternative irrigation, wastewater INTRODUCTION The increasing global population is creating a gap between water supply and demand thus threatening human consumptive use and therefore need for water conserving measures. Fresh water is a finite and vulnerable resource whose sustainability is threatened by human induced activities including domestic consumption, livestock feeding, irrigated agriculture, hydropower generation industries and aquaculture. Unreliable rainfall, multiplicity of competing uses, degradation of water sources and catchment areas all have exacerbated water use conflicts. One way of remedying the situation is the reuse of domestic wastewater for irrigation purposes. This could release

clean water for domestic use and drinking only as well as availing other alternatives especially for irrigation purpose. In developed countries where environmental standards are adhered to, much of the wastewater is treated prior to use for irrigation of pasture, parks, and seed crops and, to a limited extent, for the irrigation of orchards, vineyards, and other crops. Evidence for extensive use in developing world including Tanzania is limited (Balkema et al., 2010). Municipal treatment facilities including passage through constructed wetlands are designed to treat raw wastewater to produce a liquid effluent of suitable quality

Journal of Environment and Waste Management Vol. 2(2), pp. 047-055, February, 2015. © www.premierpublishers.org, ISSN: XXXX-XXXX

Research Article

Effect of Treated Domestic Wastewater as Source of Irrigation Water and Nutrients on Rice Performance in Morogoro, Tanzania

Nyomora AMS 047 that can be disposed off to the natural surface waters with minimum impact on human health or the environment but this can be problematic for low income countries with limited capacities for land based treatment and disposal (Balkema et al., 2010). Tanzania has insufficient water resources but has tremendous irrigation potential with some 44 million hectares (Mha) deemed suitable for irrigation; but only 10 Mha (23%) is actually cultivated and of that only 227,000 hectares (ha) is irrigated (Evans et al., 2014). This irrigation potential is not being realized due to limited financial resources capacities of the millions of smallholder farmers who constitute the majority of the agricultural sector in Tanzania. They are currently unable to take advantage of improved irrigation techniques and technologies. Of the twenty major urban water utilities in Tanzania, 11 provide some access to sewer connections. In Moshi the reported connection rate is 45%. In Morogoro the reported rate is 15% and in Dodoma and Iringa it is 13% while in Dar es Salaam the length of the sewer network is estimated at 188 km, but only 4% of households have access to it (Balkema et al., 2010; Kilobe et al., 2013). The total population of Morogoro urban is 250,000 demanding 30,000 m3 of water daily from all sources (MORUWASA, 2010). Using waste water for irrigation would remove the competition of water with urban domestic usage. However, some degree of treatment must normally be provided to raw wastewater before its use for agricultural or landscape irrigation; this strategy has received limited practice in Tanzania (Balkema et al., 2010). On the other hand, farmers around Morogoro waste stabilization ponds where the constructed wetlands were constructed already grow lowland irrigated rice using water from the Ngerengere River. The volume of water in this river diminishes during the dry season thus limiting acreage that can be cultivated otherwise due to optimal high temperatures throughout the year; it would be possible to plant and harvest rice 4 times in one year. Significant investments in infrastructure, institutions and human resources will be required to achieve the government’s stated goal of increasing the irrigated area to 7 Mha by 2015 and raising paddy yields from an average of 2 t/ha to 8 t/ha as those realized in experimental research sites (Evans et al, 2014). Constructed wetlands are designed, man-made complex of saturated substrate, with emergent and submerged vegetation, animal life, and water that simulate natural wetlands for human uses and benefits (EPA, 1993). They are relatively cost effective to establish and operate, provide effective and reliable wastewater treatment, relatively tolerant of fluctuating hydrologic and contaminant loading rates and finally provide indirect benefits such as green space, wildlife habitats and recreational and educational areas. Therefore,

wastewater that has been treated through a constructed wetland is a resource that can be used for productive uses in agriculture, aquaculture, and other activities because it contains plant nutrients like N, P, K and S that contributes to promotion of plant growth (Hussain et al.,2001). Its reuse can deliver positive benefits to farming communities, and municipalities (FAO, 2004). This study intended to evaluate the effect of constructed wetlands treated Waste Water on potential productivity of rice as an alternative solution to supplying the needed moisture and nutrients to increase rice yield productivity in Morogoro region. MATERIALS AND METHODS Study site The study was conducted in Mafisa Ward, Morogoro Urban, Tanzania (Fig 1) where MORUWASA operates its Waste Stabilization Ponds (WSP). MORUWASA-WSP collects municipal sewage and household wastewater which either flows in directly through the networked central sewer system or is emptied by tankers. The sewerage system area is situated in an undulating valley having fertile alluvial clayey soils in the lowland and farmers cultivate paddy using water from a stream that feeds into Ngerengere River. The University of Dar es Salaam-Waste Stabilization Ponds (UDSM-WSP) research group has constructed an artificial wetland that cleans wastewater intercepted from WSP No. 2 of the 6 waste water treatment ponds and delivers it to the experimental fields through closed piping. An irrigation pump with following specifications: model SE-50X; Delivery volume- 600L/min; Total head- 30M and Power speed- 2.0Kw (Fig 2) delivered waste water (WW) and tap water into the experimental bunded plots from 2 temporary reservoirs, one for WW and the other for freshwater that were dug close to the plots. Wastewater and soil samples analyses Wastewater from MORUWASA–Waste Stabilization Pond No. 2 was sampled in 1L capacity plastic containers each of which were thoroughly washed with 1M HCL and rinsed several times with deionized water prior to sample collection according to Allen (1989). Sampling was conducted using the grab method whereby WW was scooped from the pond. Samples were kept in tight bottles in an ice chest (temp =4 ºC) and immediately taken to the laboratory for further processing. The samples were then filtered and acidified to pH 2 using 6 M HNO3 and stored at 4º C for subsequent analyses of various physical-chemical parameters namely pH, EC, C.E.C, organic matter content, available phosphorus, total nitrogen, and soil texture according to APHA (1998). Soil samples from the area were collected from two

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Figure 1. A Map of Morogoro showing the site of the study area

Figure 2. Irrigation water intake and water delivery pump

points along the center-line at a depth of 0 – 10cm, and 10 – 20cm. The samples were then homogenized into a composite sample which was weighed separately, kept in polythene bags, properly sealed to prevent contamination and loss of moisture. Sub samples were derived from this composite sample for measurements of presence or absence of fecal coliform bacteria. The samples were incubated in a water bath at 44.5ºC for 24 hours where

gas production in the fermentation tube after 24 hours was considered a positive reaction, indicating presence of fecal coliform. Based on which dilutions showed positive for coliform and/or fecal coliform, a table of most probable numbers was used to estimate the coliform content of the sample plus other disease causing organisms. The results were reported as most probable number (MPN) of coliform per 100 ml (EPA, 1998).

Effect of Treated Domestic Wastewater as Source of Irrigation Water and Nutrients on Rice Performance in Morogoro, Tanzania

Nyomora AMS 049 Table 1. Physical Chemical Composition of Wastewater before passing through the constructed wetland

Parameter

Source of Sample

Anaerobic Pond Inlet Anaerobic Outlet Pond Outlet of the Last Maturation Pond

Threshold levels for irrigation water

TSS (mg/L) 250 120 50 0-2000

Phosphorus (mg/L) 2.69 2.71 2.78 10-500

Nitrates (mg/L) 0.345 0.635 0.653 50

BOD5 (mg/L) 410 150 120 200

Ammonia (mg/L) 6.07 6.24 6.05 5-50

Faecal Coliforms (MPN/100ml)

4.2 x 106 2.8 x 105 3.6 x 103 < 1000

Electric conductivity(dS/m)

0. 866 0.7-3.0

Source: Baseline data collected by CW-WSP Team, 2012: FAO (2004) for the Threshold levels

Table 2. Levels of diseases causing organisms in waste water reuse environment (Most probable number (MPN)/100ml effluent sample)

Component Total Coliforms

Fecal coliforms

Eschereia coli Salmonella Campylobacter spp.

Wastewater 1,100 210 9 ND 3

Leaf rinse water 90 3 ND ND ND

Experimental layout and design for paddy A total of 16 plots measuring 9m2 each (3m long x 3m wide) were ploughed by hand and finely cultivated into bunds. An improved rice variety [Oryzasativacv Saro 5 (TXD 306)] was used for this trial and it was sown in furrows spaced 20cm apart on 23rd August 2013. The trial was irrigated using tap water to begin with and seedlings were thinned to single plants at a spacing of 10 cm between plants. About 2 weeks after emergence on 5th September, 2013 half of the plots received an inorganic NPK fertilizer (15:9:20) at a rate of 400kg/ha and the other half of the plots received waste water (WW) treatments which were initiated on 19thSeptember, 2013. The 4 treatment combination were as follows: (i) Waste water (WW) only (ii) WW + NPK (iii) Tap water only (iv) Tap water + NPK and all the treatments were replicated 4 times in a Completely Randomized Block (RCBD) Design. WW and Tap water treatments were applied every time there was a need for irrigation, while NPK was applied only once at planting. Yield and yield components recorded and data analyses Data on yield and yield components i.e. the number of tillers, flag leaf area, flowering (%), number and length of panicle/plant, proportion of fertile and sterile grains and yield per plot were collected at appropriate times during

plant growth using the SES standard procedures (Choudhary, 1996). Analysis of variance (ANOVA) was conducted (p≤0.05) as RCBD using INSTAT software and Least Significant Difference (LSD) was computed to test for the differences between treatment means (p≤0.05) according to Gomez and Gomez (1994). RESULTS Physical-chemical-biological properties of wastewater and soils The results of the physical chemical properties of wastewater used as source of irrigation water for the experiments and soils at the experimental field are as shown in Tables 1, 2 and 3. The Initial waste water came from the 2nd maturation pond which was closest to the outlet of the anaerobic pond shown in Table 1. The values for TSS, P, Nitrates, BOC and Ammonia were similar to the typical values reported by FAO (2004). Table 3a shows the Physical-chemical properties of the soil samples collected at the experimental site i.e. pH 8.2±0.04,0.71±0.023 total nitrogen, while P was 0.5±0.03.mg/100g. The organic matter was2.3±0.08% and CEC measured to 57.9± 0.57meq/100g. The soil texture was categorized as silt loam.

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Table 3a. Physical –Chemical properties of the soil from the experimental site

Properties Mean values

pH 8.2 ±0.04 Total N(mg/1) 0.71 ±0.023 Organic matter (%) 2.3 ±0.08 P (mg/100g) 0.5 ±0.03 C.E.C (meq./100g) 57.9 ±0.57

Sand (%) 7.7 ±3.84 Silt (%) 75.7 ±17.84 Clay (%) 23.3 ±11.67

Table 3b. Heavy metalcontent in soils sampled from experimental field at Mafisa

Heavy metals Values (µg/100g) Acceptable limits(mg/kg) References

Pb bdl 20 McKeague and Wolynetz (1980)

Cr 0.05±0.01 150 Adriano (1986)

Cu 55.6±1.14 1500 McKeague(1980)

Zn 146.86±4.42 450 Adriano (1986)

Table 4. Heavy metal content of wastewater (WW) samples from MORUWASA Constructed wetland

Heavy metals Values(µg/100g) Acceptable limits(µg/l) Reference

Pb 0.01±0.003 10 (WHO-2008)

Cr 0.14±0.009 150 (WHO-2008)

Cu 6.423±0.03 2000 (WHO-2008)

Zn 59.4±0.12 3000 (WHO-2008)

Figure 3. Influence of WW and inorganic fertilizer NPK on number of tillers of rice: (a) Averaged over dates (b) Averaged over treatments

Results of heavy metals in the soil samples were as shown in Table 3b which indicated that Pb was below detection limit while Cr (0.05), Cu (55.6) and Zn (146.86)µg/100gwere below the acceptable minimum threshold limits. Similar values were found in wastewater destined for irrigating paddy.

Vegetative growth and Tillering Tillering or shooting from the stem bases started in late September, optimized in October about two months after planting, and peaked in November when the effect of treatments was evident (Fig 3a). Plants in WW treated

0

20

40

60

80

Nu

mb

er

of WW

WW+NP

Tap

Tap

Key

a

Effect of Treated Domestic Wastewater as Source of Irrigation Water and Nutrients on Rice Performance in Morogoro, Tanzania

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Figure 4. Influence of WW and inorganic fertilizer NPK on rice biomass (a) flag leaf area and (b) Wt. of Stover

Figure 5. Influence of WW and inorganic fertilizer NPK on yield components (a) Flowering %age/plant, (b) Length of inflorescence (cm) and (c) No. of spikelets/inflorescence

plots produced insignificantly higher total number of tillers per plant (48) than the Tap water irrigated plots (44) and NPK treated plots (38) while plants which received both WW and NPK produced the least number of tillers (36) (Figure 3b). Likewise the flag leaf area was insignificantly higher in WW treated (37.6 cm2) than NPK treated (34.3 cm2) and non- treated plots which were irrigated with tap

water only (29.1 cm2) (Fig 4). Figure 4b reveals that WW treated plots resulted in significantly higher biomass (straw) weight than the rest of the treatments. Biomass left over after harvest was highest in WW treated plots i.e. 2.6 ton/ha and lowest in tap water treated plots (0.8 t/ha) while in NPK treated plots it ranged between 1.1 and 1.2 ton/ha.

a

a

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Figure 6. Influence of WW and inorganic fertilizer NPK on yield components (a) No. of fertile grains/inflorescence (b) Wt. of fertile grains/inflorescence and (c) No. of sterile grains and (d) Wt of sterile grain/inflorescence

Yield components WW resulted in significantly higher flowering than other treatments. The proportion of fertile or flowering tillers/plant was significantly higher in WW treated (21.5%) than in non-treated plots (5.3%) or where WW was combined with NPK (9%) (Figure 5a). The length of flower panicles did not show any significant differences between treatments (Figure 5b) and so was the number of spikelets/inflorescence which averaged to ten (10) and the length of inflorescences which averaged 23cm (Figure 5b). The number of fertile grain/inflorescence was least in plots irrigated with tap water but was significantly higher in WW and NPK treated plots (Figure 6a). The weight of fertile grains/inflorescence followed similar trend to the numbers of fertile grains and ranged between 2.4 to 3.5g. Plots which received tap water only

produced the least number of fertile grains/inflorescence (94) weighing 2.4gm while WW treated plots averaged 135 grains/inflorescence weighing 3.5gm; similarly the number and weight of sterile grains (Figure 6c and 6d). Yield Very highly significant differences in total yield between WW treated plants and non-treated treatments were observedin this study (Figure 7). Plots which received WW only as source of irrigation water and nutrients produced 5.44 ton/ha while plots which were treated with a combination of WW and NPK produced only 1.7ton/ha. On the other hand, tap water irrigated plots but which received inorganic NPK fertilizers yielded 1.6 ton/ha while plots which were irrigated using tap water only produced only 1.3 ton/ha.

a b

c

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Figure 7. Paddy grain yield under the two sources of nutrients and irrigation water

DISCUSSION Physical chemical biological properties of wastewater and soil The soil pH averaged to 8.2± 0.04 was considered slightly alkaline. A pH between 5 and 8.5 is generally acceptable for use in irrigation; very acidic (pH less than 5), or very alkaline (pH greater than 8.5), may need to be neutralized before application as soil pH affects the availability of nutrients and other elements to plants (FAO, 2004). If pH exceeds 7.3, phosphorus is increasingly made unavailable by fixation in phosphates especially Calcium (Islam, 2013). The key nutrients in the soil N and P in the form of nitrates and phosphates were considered generally low. The organic matter content of 2.3±0.08% was considered fairly adequate and CEC which measured 57.9±was high indicating that the soil had a high capacity for holding cations. Recommended levels of Total soluble solids(TSS) for agricultural irrigation water quality standard is 0-700mg/l (FAO, 2004) which indicates that the 120mg/l soluble solids which was found in the WW from MORUWASA and used for irrigating paddy was within the acceptable concentration. The values for fecal coliforms were higher than the threshold values recommended of less than 1000MPN/100ml WW. After passing the wastewater through the constructed wetland, table 2 shows the disease causing organisms in waste water and plant parts as an indicator for the health concerns of stakeholders (operators, farmers and consumers). The total coliforms were slightly higher than the acceptable values while the fecal coliforms were not. Vegetative Growth and Yield There was a trend for greener and more luxurious plant

growth in all plots that were irrigated using WW followed by plots that were irrigated with tap water but which also received inorganic fertilizers. WW only treated plots also flowered slightly later than plots that were irrigated using tap water only. Waste water previously treated in a constructed wasteland promoted vegetative growth, tillering, and biomass production of this rice variety much more than non-treated plots or those treated with NPK or their combination in that order indicating the effectiveness of WW in realization of the yield potential of rice- variety Saro 5. Tillering is an essential yield component used to determine the overall architecture of cereal crops and therefore is an important agronomic trait for rice grain production. It is a specialized grain bearing branch that is formed on un-elongated basal internode and grows independently of the mother stem or culm by means of its own adventitious roots. The inflorescence are born on fertile tillers so by promoting these inflorescence bearing tillers using WW in the current study, it was evident that WW potentially effected paddy productivity. There was a tendency of increased production of sterile grains in WW treated plots in comparison to other treatments but this was masked by the higher production of fertile grains. Response of other paddy yield components including the flag leaf area, flowering %, the number and length of spikelets were similar to that of tillering confirming the effectiveness of WW as a good source of irrigation water and nutrients for high productivity. In rice, the flag leaf area is the most metabolically active organ that supplies photosynthates to the developing grain and therefore it plays a big role in grain yield as also suggested by Prakash (2012). This was highly promoted by WW treatment alone while the combination of WW and NPK was not as effective especially for flowering, grain size and total yield indicative of nutrients overload.

Effect of Treated Domestic Wastewater as Source of Irrigation Water and Nutrients on Rice Performance in Morogoro, Tanzania

J. Environ. Waste Manag. 054 Effectiveness of Constructed wetland in supplying nutrient rich WW Irrigating using municipal treated wastewater can conserve water and fertilize crops economically by capturing nutrients that would normally be wasted. This irrigation method is also an effective way to prevent contamination of nearby waterways with the disease organisms that wastewater contains, hence a considerable health benefit. However, reuse of wastewater for agricultural irrigation, industrial reuse and ground water recharge can become a risky endeavor if prior evaluation of residual contamination of nutrients (high N and P), organics, toxic, trace elements and some enteric bacteria and virus and monitoring is not regularly done (Kivaisi, 2001); as well as converting harmful substances to harmless components or to acceptable concentration that can be assimilated into the receiving waters without environmental damage. In studies utilizing several Municipal and agriculture wastewater discharge have been found to contain elevated nutrient concentrations (N and P) that may stimulate excessive or nuisance algal growth in downstream receiving waters (Kivaisi, 2001). On the other hand, chemicals (organic, inorganic and heavy metals) in wastewater that passes through a wetland ecosystem is rapidly inter-converted from organic to inorganic forms and forms of chemical complexes that in turn maybe adsorbed or precipitated within the wetland (Musiwa, 2001). Wastewater treatment cost studies show that marginal costs are very high at higher levels of treatment (Schleich et al., 1996). However, these higher marginal treatment costs may sometimes be justifiable in view of the value of the crop, degree of water scarcity, and public concern. In the current study, tap water only irrigated plots produced 1.3 ton/ha which was far below the yield potential of Saro5 rice variety of 8-10 ton/ha. WW only treated plots promoted yields which was within the yield potential of Saro 5 while a combination of WW and NPK depressed yield potential of Saro 5 to only 1.7 ton/ha. Other research studies (Kanyeka, 2013) had shown that Saro 5 is an open pollinated rice variety grown both in lowland rainfed and irrigated systems in Tanzania. It has a high tillering ability with a range of 30 to 50 tillers/plant with a high yielding potential of 8‐ 10 ton/ha at r

esearch station and 4‐ 6.5 ton/ha in farmer’s field. Most local varieties in Tanzania produce

10 ‐15 tillers that give total yield of 1.8 ton/ ha due to their low yielding abilities (Kanyeka, 2013). The current study results on the number of tillers and yield/ha especially in the WW treated plots were within the yield potential of this variety. NPK applied once at planting at a rate of 400kg/ha added yields of only 0.4ton/ha in excess to that realized under tap water. At the current price of 54,000TShs/50 kg bag

of NPK fertilizer, this translates into 432,000 Tanzanian shillings/ha. Therefore, based on the extra price tag of the inorganic fertilizer, it pays to irrigate rice fields using WW from CW when it is available. This is in addition to getting an extra source of irrigation water. FAO (2004) had estimated that a city with a population of 500,000 and water consumption of 200 l/day per person would produce approximately 85,000 m3/dayor 30 m³/year of wastewater, assuming 85% inflow to the public sewerage system. If treated wastewater effluent is used in carefully controlled irrigation at an application rate of 5000 m3/ha/year, an area of some 6,000 ha could be irrigated. In addition to this economic benefit of the water, the fertilizer value of the effluent in the range of 50 mg/l Nitrogen, 10 mg/l Phosphorus and 30mg/l Potassium would be supplied. Assuming the application rate of 5,000 m3/ha/year the fertilizer contribution of theeffluent would be: 250 kg/ha N, 50 kg/ha P and150 kg/ha K per year which is quite substantial. Constructed wetlands systems are technically a good option to realize hygienic sanitation as the reduction of faecal coliform is high. Faecal coliform removal in constructed wetlands in Tanzania has been determined and found to be greater than 99% during 5 case studies (de Ruijter 2009). In practice, most developing countries use untreated wastewater for agriculture for a variety of reasons, least of which is the cost of treatment and the loss of precious nutrients. However, treatment of wastewater prior to agricultural use is believed to be essential: first, from the point of view of public health protection, and second, to respect local social and religious beliefs (Mara 2000). In view of these requirements, water scarcity, dry land farming, hot climatic conditions, and the high economic value of fresh water resources, a great deal of research and development efforts needs to be undertaken, for the reuse of wastewater. More studied are needed to concretize the health status of farmers handling irrigation using WW as well as consumers of rice grown in the study area under this system. ACKNOWLEDGEMENT The author acknowledges the financial support offered by the Centre for Science and Technology, Tanzania (COSTECH) and logistical contributions of other researchers in the team REFERENCES Adriano DC (1986).Trace elements in the terrestrial

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Accepted 19 January, 2015. Citation: Nyomora AMS (2015). Effect of treated domestic wastewater as source of irrigation water and nutrients on rice performance in Morogoro, Tanzania. Journal of Environment and Waste Management 2(2): 047-055.

Copyright: © 2014 Nyomora AMS. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.