Urban Sanitation in Bangladesh - Component 4: Treatment, disposal and reuse


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Every garbage dump is an investment

Our SNV learning and demonstration project started with the capacity building of the local government (component 3), aiming to create a climate of good governance for safe emptying, and to raise demand and supply for safe sanitation (see component 1 and component 2). Our efforts went further, to be able to meet increased demand for safe sanitation services (component 4). You know, it’s like the chicken and the egg, the one cannot do without the other, and wondering what comes first is fairly useless.

In 2015, the BMGF provided funds for a treatment plant that could process up to 15% of sludge generation in Khulna. This treatment plant can be expanded step by step as demand grows. Ultimately, the investment costs for universal coverage in sludge treatment for Khulna are estimated at five (5) million dollars. Compare this to the whopping 158 million dollar needed for a sewage based investment that would cover a mere 60% of Khulna (KWASA 2017). This tremendous cost difference stems from the fact that most households have built pits or septic tanks to collect their faecal sludge, for lack of sewage. We took this existing situation as a starting point for our approach. The enormous cost difference between sewerage and on site solutions has also been found in other places, as this report by BMGF shows. 

Although treating faecal sludge on-site requires considerably less funds than building a sewage system from scratch, the necessary investment is still considerable for cities in this region. Technical options were therefore prepared and selected in a process of informed choice, taking into account wastewater and/or sludge volumes, their characteristics, and re-use potential.

4.1 Field survey: Providing sludge Characteristics

We are in deep shit, and we must stop ignoring it

Before advancing on the construction of a treatment facility, we gathered field data that would help us to create the right design of the plant. First, we calculated the quantity of the sludge. According to the field survey the faecal sludge volume generated in Khulna, Jhenaidah and Kushtia is respectively 710,000 m3; 58,705 m3; and 104,581 m3 per year.

Just to give you an idea of what we are talking about; the Shanghai tower is one of the highest towers in the world, counting at 630 meters. Imagine a slightly bigger tower, just as broad and deep as it is high - there’s your annual faecal sludge for the city of Khulna alone. And on the list of cities in the developing world, Khulna is small scale compared to the rest. In 2016 the world counted 31 megacities with over 10 million inhabitants (24 in the less developed world) and over 1.000 cities with over 500.000 inhabitants each. Almost one quarter of the global population lives in cities with over 1 million inhabitants. And in many of these cities, sanitation is not managed properly. In other words, we are literally drowning in a sea of shit. And whereas the Shanghai tower reaches out its bright and shiny pinnacle towards the skies, this murky sea flows underground, contaminating its surroundings unseen, and creating a vicious cycle of disease; diarrhoea, malnourishment; while locking people into life-long disadvantages such as poor physical growth, hampered cognitive development, less earning potential and ill-health. This is why we need to close the sanitation gap.

How about the characteristics of the faecal sludge? We literally went out into the fields to collect samples of sludge for each of the three municipalities involved in this project. Characteristics were determined for each sample, experiments were performed on sixteen wastewater quality parameters, such as; solids concentration, chemical oxygen demand (COD), biochemical oxygen demand (BOD5), nutrients, pathogens, etc.

Let us dazzle you sanitation nerds with a few facts: “The Solid contents in faecal sludge of the three towns varied between 3% and 6%. The range of COD concentrations were 7600-9600 mg/L. BOD5 concentrations were a whopping 819-1662 mg/L, whereas the acceptable limit for disposal into inland water bodies is only 40 mg/L (ECR, 1997). Thus, it was a significant challenge to reduce the BOD5 in the faecal sludge treatment plant for its ultimate disposal.”

Put simply, if waste contains a lot of organic material, you can decompose it naturally by using specific plants that accelerate the process. The end result can be used as a soil conditioner. But if the waste contains a lot of chemicals you need to add extra treatment to the process – as is the case in Europe where waste is bubbling with chemicals from shampoos and soap, because all the wastewater is collected together. In Bangladesh, where wastewater from tap and septic tanks is collected separately, faecal sludge mainly consists of organic material. Which by the way does not mean that it is free of pathogens, it is just easy to decompose in an organic way.

4.2 Feasibility Study: selecting the right technical option for the plant

The organic way; letting rocks, sand and flowers quietly decompose sludge

A feasibility study was conducted for all three towns on a short term faecal sludge treatment plant (FSTP). The Khulna University of Engineering & Technology (KUET), the Asian Institute of Technology (AIT) and University of Science and Technology Beijing (USTB) jointly analysed the current context of these towns and cities in terms of their population, land use and sludge volume. We used these results to support the city authorities decision on design, construction and operation & maintenance of short-term treatment options.

Our scientific partners helped us to point out the technical options for the treatment plant, and from these options the city council chose ‘constructed wetlands’ for Khulna and Jhenaidah, because of their low capital and running costs. Kushtia already had a drying bed with co-compost facilities. Jhenaidah had a non- functional plant.

Just to give you an idea, alternative solutions would have been: a biogas installation, waste stabilisation ponds or an omni processor (that is high tech dewatering technology, using biosolids to produce electricity and clean drinking water as output. Want to see Bill Gates drink water from human waste? See this video.

So, what is a constructed wetland? First you need to know that Bangladesh is one of the largest fish exporters in the world. The population knows all about digging ponds and using natural functions of vegetation, soil and organisms to keep the water healthy. We used this expertise to build the basins. 

We surrounded the basins with dykes, that we lined with plastic sheets to prevent infiltration; these were weather proof plastic high-density polyethylene - HDPE- sheets. Then we filled the basins with layers of small rocks, brick chips, plus sand on top to filter the incoming sludge. We collected the filtered liquid (called percolate) with a piping system and further treated it in a second pond. As time goes by, these liquids contain less and less pollutants until the water can safely be disposed in the nearest canal, thereby complying with the National Standard.

The biosolid ground was planted with special flowers that can withstand the high level of pollutants in the sludge. These plants speed up the decomposition of the sludge. After four years the sludge will be fully decomposed, and will no longer contain harmful elements. Better even, nutrients in the remaining soil can be safely re-used as soil conditioner or bio briquettes. By the way, re-using sludge is something we do in Kenya as well, with the support from the European Commission.

Because the plant is just a first step towards city wide waste treatment, we call it a short term treatment option. In the future, long term treatment options will have to be developed to cater sanitation services for the entire city. This can be done either by developing several smaller treatment units, or by going for one centralised system. The latter will require more upfront investments at once which is a challenge for the cities.

 

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