Wastewater reuse for vegetable growing

Effects of using wastewater on vegetable growing and the associated socio-economic impacts on farmers in the Kafue Lagoon Areas and along Ngwerere River

(Draft final report) ByCharles Bwalya Chisanga and Oscar Musweu Silembo

Report PMA 14;September 2004

Ministry of Finance and National Planning Zambia Social Investment Fund

Executive Summary

This report is an out from Poverty Monitoring Analysis (PMA) under the Zambia Social Investment Fund (Zamsif). The aim of the study was to assess the Effects of using wastewater on vegetable growing and the associated socio-economic impacts on farmers in the Kafue Lagoon Areas and along Ngwerere River. The research is based on field studies carried out in Kafue Lagoon and in the Ngwerere sub-catchment.

In urban and peri-urban areas in developing countries such as Zambia, poor farmers commonly use wastewater to irrigate high-value crops. In many places the pre-treated or untreated wastewater is their only source of irrigation water—so their livelihoods depend on it. But, as well as bringing benefits, the unregulated use of wastewater or nutrient enriched water also poses risks to human health and the environment. Wastewater irrigation can also significantly contribute to household and urban food security and nutrition. Recent studies conducted in several Asian and African cities have revealed that wastewater agriculture has accounted for over 50% of urban vegetable supply. Wastewater is used as a source of irrigation water as well as a source of plant nutrients and trace elements allowing farmers to reduce or even eliminate the purchase of fertilisers. One tenth or more of the world’s population currently eats food produced on wastewater but not always in a safe way.

The sources of wastewater are made up of domestic wastewater, industrial wastewater, storm-water and groundwater seepage entering municipal sewage network. Domestic wastewater is made up of effluent discharge from household, institutions, and commercial buildings. Industrial wastewater is the effluent discharged by manufacturing plants. Wastewater is composed of organic matter, nutrients, inorganic matter, toxic chemicals and pathogens. In many place the wastewater is discharged into water bodies or the environment treated or pre-treated or as raw sewage.

The study was carried out in two phases within a period of two months.

Ø  Document review on wastewater reuse

Ø  The samples were tested for microbiological (total coliform, E. coli and faecal streptococci), physicochemical and heavy metals quality parameters, plant and riverbed sediment samples were also collected and tested for heavy metals. The plants and sediment analysis were for exploratory purposes.

Ø  Questionnaire formulation and administering in Ngwerere River and Kafue Lagoon Areas. Questionnaires were analysed using excel, graphs and figures.

Literature review

Westcot (1997) makes a distinction between direct and in-direct reuse. Direct reuse is the planned use of raw or treated wastewater, where control exits over the conveyance of wastewater from the point of collection or discharge from a treatment plant to a controlled area where it is used for irrigation. This is the situation in many developed nations. Indirect reuse is the situation found in many developing national like Zambia where municipal and industrial wastewater is discharged without treatment or monitoring into the watercourses draining an urban area. There is no control over the use of water for irrigation.

Microbiological contamination: The WHO guidelines provide a limit for permissible levels of microbiological contamination in water. Westcot (1997) addresses the question how the WHO guidelines can be applied where farmers are irrigating using water from rivers downstream of large urban centres. He suggests that in the absence of better information it is prudent to use the WHO standard for faecal coliforms as the quality standard. He also suggests establishing a routine water quality-monitoring programme, based on faecal coliforms number to support certification programme for high risk or restricted crops. This requires education of consumers and encouraging market forces whereby consumers chose to buy certified produce. It is argued that this approach is more realistic than attempting to impose crop restrictions which also almost impossible to enforce. The wastewater can be used for unrestricted irrigation of crops such as lettuce, salads and cucumbers grown for direct human consumption and eaten raw and for restricted irrigation of crops not intended for direct human consumption such as cotton, sisal, wheat and sunflower. The criteria for unrestricted irrigation contain the same helminthes criteria for restricted irrigation, in addition to a restriction of £1000 faecal coliforms per 100ml treated effluents. Restricted irrigation refers to the irrigation of crops not intended for direct human consumption and there should be £1 human intestinal nematode egg per liter implying a greater than 99% treatment level. Reuse of (pre) treated wastewater, especially in agriculture, could considerably contribute to water resources conservation, recycling of nutrients and prevention of surface water pollution. Water quality guidelines are necessary for wastewater irrigation, but they are rather strict and developing countries cannot afford the expensive treatment.

Trace elements and heavy metals: It is widely accepted that levels of trace elements and heavy metals in irrigation water are likely to be toxic to plants in concentration below that which may pose a profound risk to human health and provides a degree of natural protection to irrigators. This study focused on heavy metal in the water, plant tissue and sediments. The findings indicate that the heavy metals in water were below the detection limit. Some of the heavy metals were found in the plants such as lead, zinc and cadmium. Copper and mercury were not detected in both the water column and plant tissues. Compared with the thresholds for plants the heavy metals in plants are below the limits, which may be harm to human health.

Farmer characteristics

Gender

In Kafue Lagoon area, 60% of the peasant farmers using wastewater are women and 40% are men. By contrast the majority of the farmers in Ngwerere area are men (81%) and 19% are women.

Age

The average age of farmers in Kafue Lagoon areas is 35 years whist in the Ngwerere is 30 years. Most farmers engaged in farming in the Ngwerere don’t stay near the river and others rent the plots and pay K60, 000 after six (6) months. In the Lagoon areas farmers don’t pay any thing for farming within the area.

Other occupation

The main occupation of farmers in Kafue Lagoon area is farming and gardening (100%) since all of the respondents interviewed are unemployed. In the Ngwerere area the main occupation of the farmers are also gardening and farming which is 77%.

Land tenure

The land tenure in Ngwerere River Area is communal, leasehold, farmer own land and Zambia National Services. In the Kafue Lagoon areas the land tenure is freehold, effluent discharge area for Lee Yeast, Nitrogen Chemicals of Zambia and Shikoswe stream  before the effluents enter the Kafue River.

Irrigation water management

The sources of irrigation water for farmers in the Kafue Lagoon areas are the Shikoswe stream, Nitrogen Chemicals of Zambia and Lee Yeast effluent discharge canals. In the Ngwerere sub-catchment the sources of water is a permanent stream running within the catchment.

The most common method used by farmers (100%) in the Lagoon areas to irrigate their field crops is by using containers or buckets  (10 to 20 litre containers). Even though this is a labour intensive method, some farmers are able to apply nearly to the entire field. The respondents interviewed in Ngwerere River area irrigate their crops manually using bucket/watering can (10 to 20 litre containers) (93%) and 7% of the respondents use pumps to convey the water from the river channel on to their crop fields.

Cropping practices and yields

The size of land preparation varies greatly between sites. The average plot size for the surveyed farms (small-scale peasant farmers) in Ngwerere area is 0.25 ha and ranges from 0.1 ha to 0.5 ha whilst in Kafue Lagoon is 1.2 ha and ranges from 0.25 ha to 2 ha respectively. The mostly widely grown crops vary within the study areas. Rape and chinese cabbage are the most common grown crops in both areas. In addition to Kafue Lagoon areas farmers also grow sugar canes, which are sold in Lusaka, Chirundu and other areas. In the Ngwerere a large variety of other crops are grown in addition to rape and chinese cabbage. The average income realised from the sale of the produce in both areas vary tremendously. In the Lagoon areas the average incomer per year varies from K 800, 000 to K1, 000, 000 and in the Ngwerere is K800, 000 to K2, 400, 000. There appear to be a clear need for extension services to growers along side with improving the water quality.

Marketing

The single most common means of marketing the produce by farmers is to take their products to the markets. Farmers from the Ngwerere area sale their produce individually at Soweto, Town Centre, Kabanana, Chipata Compund, Ngombe, Katabalala, Chaisa, Garden, and Kaunda Square markets. The crops are marketed individually (83%) or as a formal group (12%) or traders (3%) buy the produce from the farmers, which they later sell.

The single most common means by farmers to market their produce in the Kafue Lagoon is for growers to sale their produce as individuals and this is at 100%. Individual farmers market the produce of the Kafue Lagoon by taking them to the markets. There are sold in different parts of Kafue and Lusaka including Chirundu.

Public health

The diseases, which are prevalent in the two study areas, are malaria, bilharzias and diarrhoea. For the Ngwerere area, secondary data obtained at Kasisi Rural Health Centre helped to confirm the findings

Water quality:

Plant analysis: heavy metals were not detected in mercury and copper. Lead, zinc and cadmium were detected. Compared with the threshold values the value for lead, zinc and cadmium do not pose any risk to human health.

Physicochemical parameters: For Ngwerere river area the physicochemical results were within the limits of the ECZ, WHO, DWA and EU guidelines for water quality. However, the pH was higher than the recommended upper limit of 9 in some cases. Ammonia levels at N1 and N2 (that is urban and peri-urban areas) was higher than the WHO drinking water guideline value of 0.5mg/l. On average sodium was higher than the guideline value of 200mg/l which can lead to the problem of specific ion toxicity and salinity problems. Total suspended solids (TSS) at N1 and N3 were also higher than the ECZ guideline value of 100mg/l.

The conductivity, phosphorus and calcium levels at Lee Yeast sampling point were higher than the recommended standard by ECZ. High calcium and conductivity levels were also reported by Sinkala et al (1996). The source of the calcium is mainly the geology of the area. The high conductivity corresponds to high sodium content of the effluent.

The Shikoswe effluent had relatively high levels of ammonia and phosphate, the reason being that it carries mainly sewage effluents.

All the other parameters measured were lower than the recommended maximum concentration in irrigation water, according to Pescod (1997). The concentration of heavy metals and boron in the water at all the sampling points were below the detection limit of the method of analysis which is also far below the recommended maximum concentrations

Sediments: Two samples were collected on different days at both sites. After about a week, there was a high increase in the concentration of Zn, Fe, Pb and Cu at the first two sites (N1 and N2) on the Ngwerere River. At Kafue lagoon, there was also an increase in the heavy metal content after 12 days at the Shikoswe stream site, also indicating a relatively high rate of deposition. The results from the sediments samples during the study period were compared with the standards in the Netherlands.

Microbiological: For Ngwerere River only the last point (N3 about 23 km from source) qualifies for unrestricted irrigation according to the WHO guideline value of £1000 faecal coliform/100ml. Under unrestricted irrigation vegetables and salad crops can be grown using water with £1000 faecal coliform/100ml. Therefore, the growing of vegetables at the other sites (N1 and N2) poses a health risk to workers (or producers) and the consumers due to high levels of faecal coliforms.

Kafue Lagoon Areas, the Shikoswe and Lee Yeast effluent streams the values for faecal coliforms were above the WHO guideline of £1000 faecal coliforms/100ml

Summary of the conclusions.

Ø  The WHO guidelines for microbiological quality of wastewater use/or reuse for irrigation are intended as a guide for the design of treatment plants

Ø  There is no evidence of pollution with heavy metals that may pose a threat to irrigated crops

Ø  Farmers are irrigating their crops using the water in the Ngwerere River and Kafue Lagoon Areas as a means of earning a living

Ø  All the respondents interviewed in the Lagoons are unemployed while 87% of the respondents in Ngwerere are unemployed

Ø  Water salinity may pose a threat to crop production in both areas

Ø  There is also need to embark on an education programme for farmers and the public

Using the WHO guidelines only restricted irrigation can be practiced