Sewage Pre-Treatment

In warm climates, wastewater treatment using anaerobic (no oxygen present) biological processes, have the advantage of efficiently reducing the organic material in municipal wastewaters and producing energy in the form of biogas. One promising technology is to integrate membrane filtration with anaerobic treatment in an anaerobic membrane bioreactor (AnMBR).

Energy recovery is an intrinsic part of anaerobic technology. Through biological conversions, the energy contained in organic components is released in the form of raw biogas. This biogas is used as fuel for a solid oxide fuel cell (SOFC) that produces electricity. By using this approach high quality energy is generated which supports the energy demand of this first treatment step. 

AnMBRs have a small footprint and can treat concentrated wastewaters making them suitable for urban environments. AnMBRs are known for producing particle free high quality effluent that is suitable for other treatment processes. Despite these advantages, one of the major problems is the relatively large (costly) membrane area required to sustain stable operation. As a consequence AnMBRs typically do not handle large fluctuations in water inflow rates.

Because New Delhi experiences monsoons, high water flows are expected and have to be dealt with. Through exploring and developing additional separation technologies namely dissolved air flotation (DAF), this research project seeks to maintain the superior effluent quality of AnMBRs by dealing with the fluctuation in water inflow rates while remaining cost effective.

The removal and conversion of organic material is the important first step in wastewater treatment systems. Organic solids or particulate material could cause unwanted biological activity in other treatment processes and pose severe health risks. Anaerobic membrane bio reactors (AnMBRs) are a proven technology that can produce particle free water and biogas.

The research focus will be on ensuring optimal performance of the membrane filters that are prone to clogging. Methods such as below critical flux operation (i.e. filtrate flux above which irreversible deposits take place), periodic back washing, chemical cleaning and improving surface properties of the membranes will be investigated.   

The energy that is contained in the biogas can be recovered using solid oxide fuel cells (SOFC). Biogas typically contains methane (CH₄), nitrogen (N₂) and carbon dioxide (CO₂) along with other pollutants such as hydrogen sulphide (H₂S), siloxanes and volatile organic compounds. These compounds can damage part of the SOFC and reduce long term performance. Initial research will focus on testing the SOFC with different biogas compositions and the removal of pollutants in the biogas. Another research focus is on making the biogas suitable for direct injection into the fuel cell.

To be able to cope with fluctuating water flows and solids concentrations, water and (organic) particles, have to be separated. The separation technology, dissolved air flotation (DAF) will be used for this purpose. Since DAF uses air bubbles to separate organic solids from the water, oxygen toxicity might be a problem for the anaerobic (no oxygen) bacteria that live in the anaerobic reactor. For this reason research will focus on the effect of oxygen in anaerobic systems and developing alternative gas carriers such as biogas.

For the development and construction of a suitable pilot scale pre-treatment system several steps are needed. Initially, a small scale installation (up to 100 liters per day) is tested with Barapullah drain water. During this initial period, the main focus is on the interaction between the separation and conversion systems. The information obtained from the small scale installation can be used to develop improved process designs.

Next, the improved process designs from the initial phase are used to scale up to 10.000L per day installations. At this stage a robust and high rate anaerobic process combined with a system that can effectively separate solids and liquid will be built based on membrane filtration and or DAF.

Safe reuse of effluent

By developing robust systems that ensures reliable first source of water, we contribute to making water reuse possible and applicable in various locations. The anaerobic membrane technology produces organic material free and nutrient rich irrigation water which could be used for farming after the water quality aspects are addressed (project 1B). 

Source of income

The recovery of additional “value-added” by products could make the system very interesting in a local resource recovery perspective. The biogas utilization efficiency can be doubled using SOFCs, making the treatment more energy efficient. Also, the sludge (bacterial slurry) produced in the anaerobic treatment can be used locally for the production of activated carbon or in as partial replacement of clay in making bricks and tiles suitable for construction.

Knowledge creation & dissemination

Our goal is to create a robust wastewater pre-treatment system that can be used in an urban context. By actual demonstration of robust wastewater pre-treatment technology in an urban context we contribute to the success of future water reclamation projects.