A Better World - Volume 3: Ensure Access to Water and Sanitation for All

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access

water

and

sanitation

for

all

Indeed, raw wastewater irrigation is a centuries-old practice,

particularly in the dry summer months. Now, however, market

demand, soil health, rainfall patterns, and the characteristics

of the wastewater itself, have changed, making it necessary to

question this ancient practice.

Apart from nutrients such as nitrogen, sulphate and

phosphate, raw wastewater often contains pathogens, salt,

suspended solids, xenobiotics and heavy metals, although

wastewater generated by resource-poor semi-arid tropical

villages rarely shows heavy metal contamination comparable

to urban or peri-urban wastewater. The salt and suspended

solid deposits can significantly deteriorate the physical

property and fertility of the soil exposed to prolonged raw

wastewater irrigation, particularly in the semi-arid tropics

where rainfall is often too little to wash the contaminants

from the top soil through run-off.

The pathogens present in wastewater pose a risk to the

farmer, consumer and other stakeholders in the value chain,

particularly when salad crops and vegetables are grown

using raw wastewater. Many farmers accept the health risks

of parasitic worms, protozoa, viruses, and bacteria as occu-

pational hazards as they cannot afford treatment for some

of the health problems caused by exposure. Farmers irrigat-

ing with wastewater tend to have higher rates of helminth

infection than those using freshwater.

Infection to skin and

nails may also occur among these farmers.

In the absence

of proper labelling, consumers and retailers often remain

unaware of the health risks of such pathogen-infected farm

produce, for instance helminth infections.

The potential of constructed wetland to enable better

rural wastewater management

It is estimated that, unlike developed nations which treat

about 70% of their wastewater, the treatment capacity of

countries located in the semi-arid tropics is between 8 and

28%.

Conventional sewage technologies, which are diffi-

cult to maintain and operate to full capacity even in urban

environments, seem unlikely to be the solution to wastewater

pollution in resource-scarce villages.

Constructed wetlands

(CW) are considered to be a technical, economical, and envi-

ronmentally sustainable solution for wastewater treatment

in small communities since they are efficient in removing

diverse pollutants.

The various types of CWs used over

the last four decades can be grouped into two broad catego-

ries: Free Water Surface (FWS) wetlands, which involve the

use of a pond, and Subsurface Flow (SSF) wetlands, which

make use of dry surfaces. One major advantage of SSF-CWs,

though slightly more expensive than FWS-CWs due to the

cost of the filtering medium, is better control of mosquitos.

Despite their apparent simplicity, CWs are complex ecosys-

tems created and influenced by many physical, chemical and

biological processes. The CWs involve basic biogeochemi-

cal processes such as filtration, sedimentation, plant uptake

or phytoremediation and microbial degradation in remov-

ing contaminants from wastewater. Such systems, devoid of

chemicals and moving mechanical parts, have a low operat-

ing and maintenance cost. As common gardening skills are

sufficient to maintain the system, CWs are a feasible waste-

water management solution for small, rural communities

with a limited power supply and resources.

The performance of CWs is being evaluated in the

field as part of an ongoing Indo-European Union project,

Water4Crops, funded by the Department of Biotechnology,

Government of India (

€

3 million) and the European Union’s

Seventh Framework program (FP7) (

€

6 million). The project

has involved 22 European and 12 Indian partners. The exper-

imental facility at ICRISAT provided scope to compare the

phytoremediation potential of several macrophytes in differ-

ent combinations over a period of three years for the greywater

generated by a nearby urban household. A total of twelve

constructed wetlands sown with different plant species:

Typha

latifolia

Cana indica

Cymbopogon sp

Pennisetum purpureum

Pennisetum americanum

Brachiaria

mutica

, and floating macrophytes such as

Eichornea crassipes

and

Pistia stratiotes

were evaluated. Studies with SSF

as well

as FWS-CWs

have clearly shown potential. SSF-CWs sown

with

Typha latifolia

and/or

Cana indica

were found to be the

most efficient and flexible and were subsequently scaled-up.

Demonstration of constructed wetland in villages

The scaling up of CWs in different villages has been carried

out as part of various developmental projects supported by

the Indian government and Corporate Social Responsibility

projects (Table 1) to reveal possible bottlenecks at a techni-

cal, social or policy level. The existing trust base in different

watersheds towards scientific development has now given the

confidence for CWs to be used for the treatment of wastewa-

ter in these villages. The scaling up process involves several

stages including an awareness campaign, site selection,

construction, commissioning and the reuse of treated waste-

water for safe irrigation practices. In the watershed villages,

construction and commissioning was carried out involving

local NGOs, partners and villagers. The activity was selected

as part of an ongoing project, named

Bhoo-Samrudhi

, and was

funded by the Government of Karnataka. The site-selection

and design of suitable locations in various districts covered

under the project were provided to the district authorities

by the Panchayat Raj Engineering Department, Karnataka.

Constructed wetlands are the one of the most cost-effective solutions for

treating wastewater at community level

Treated water

Filter bed

consisting of layers

of gravel and sand

Wastewater

inlet

Image: ICRISAT