Recent Advances in Sewage Treatment

RECENT ADVANCES IN SEWAGE TREATMENT

• Membrane Aerated Biofilm Reactors (MABR)

• Anaerobic Membrane Bioreactor

• Aerobic Granular Sludge

• Membrane Fuel Cells

 

Membrane Aerated Biofilm Reactor

Membrane Aerated Biofilm Reactor (MABR) technology provides a revolutionary improvement in aerobic wastewater treatment for a number of reasons, particularly its high energy efficiency and increased treatment capacity, compared to traditional wastewater treatment systems.

Much of the energy used in aerobic treatment is tied to aeration, the introduction of air bubbles into wastewater via pumps, paddles, and other mechanisms. This enables aerobic bacteria to digest waste, but aeration can be very inefficient, so reducing this massive energy consumption is a major goal.

MABR represents one such technological breakthrough. MABR systems passively circulate oxygen through a spirally wound membrane at atmospheric pressure. MABR's self-respiring membrane allows bacteria to consume oxygen more readily for a 90% reduction in energy used for aeration.

What's more, the membrane surface quickly accumulates a biofilm of bacteria that establishes a Simultaneous Nitrification-Denitrification (SND) process to produce a high- quality, low-nitrogen effluent suitable for reuse in irrigation. The MABR process is also low-maintenance. All of these advantages add to an overall reduction in energy use.

 

Anaerobic Membrane Bioreactor

An MBR system combines anaerobic digestion with physical separation membranes, resulting in maximum organic load removal and biogas production. The technology produces a superior effluent quality compared to any anaerobic technology on the market.

An MBR is ideally suited for treating wastewater streams or slurries with very high concentrations of organics, solids, and fat, oil, and grease (FOG). The membrane barriers ensure complete solids retention, efficient system operation, and process stability at all times even under peak hydraulic and organic loading conditions. Since gravity settling is not required, higher organic loadings and mixing intensities can be employed than with other anaerobic technologies.

To increase loading capacity and improve performance and effluent quality, existing anaerobic systems can easily be upgraded to an An MBR. The system can also be paired with an ADIR aerobic membrane bioreactor (MBR) to provide complete treatment and meet even the strictest discharge requirements.

COST SAVINGS

• Minimize sludge handling and disposal costs\

•  Save on energy costs:

• Significantly less energy-intensive than aerobic systems

• Biogas can be utilized to reduce fossil fuel consumption

• Minimize aerobic polishing requirements

• Eliminate primary treatment and wastewater surcharges

• Reduce or eliminate chemical usage

 

PROCESS ADVANTAGES

• Membrane barrier ensures complete solids retention and process stability

• Large biomass inventory ensures efficient treatment at all times

• Minimal pre-treatment and post-treatment (aerobic polishing) requirements

• Eliminates issues with gravity clarification

• Handles high organic loadings and mixing intensities

• Can digest high amounts of solids and FOG

 

ENVIRONMENTAL BENEFITS

• Consistent, high quality effluent

• Very low BOD

• Free of TSS

• Continuously meet discharge requirements

• Small footprint

• Convert organic waste to recoverable green energy (heat and power)

• Waste sludge suitable for land application

• Improve local and global water security

 

SIMPLIFIED OPERATION & MAINTENANCE

• Minimal operator attention

• Reduced sludge handling

• Superior membrane durability and performance with low maintenance:

• Long lifetime

• Simple, infrequent cleaning procedure

• Membranes are cleaned in place

 

Aerobic Granular Sludge Technology

Aerobic Granular Sludge Technology is an innovative biological wastewater treatment technology that provides advanced treatment using the unique features of aerobic granular biomass. The unique process features of the technology translate into a flexible and compact process that offers energy efficiency and significantly lower chemical consumption.

HOW IT WORKS

Batch Cycle Structure

Based on the unique characteristics of granular biomass, the Aerobic Granular Sludge Technology uses an optimized batch cycle structure. There are three main phases of the cycle to meet advanced wastewater treatment objectives (Fill/Draw, React, Settling). The duration of the phases will be based upon the specific waste characteristics, the flow and 

FEATURES & SPECIFICATIONS

• Robust structure of granule withstands fluctuations in chemical spikes, load, salt, pH and toxic shocks.

• No secondary clarifiers, selectors, separate compartments, or return sludge pumping stations.

• Settling properties at SVI values of 30-50 mL/g allow MLSS concentrations of 8,000 mg/l or greater.

• Proven Enhanced Nutrient Removal (ENR).

• Simplified operation with fully automated controls.

BENEFITS

• Optimal biological treatment is accomplished in one effective aeration step.

• Four times less space required compared to conventional activated sludge systems.

• Energy savings up to 50% compared to activated sludge processes.

• Robust process without a carrier.

• Significant reduction of chemicals for nutrient removal due to the layered structure and biopolymer backbone of the granule.

• Lowest life-cycle cost.

 

Microbial Fuel Cells

A Microbial Fuel Cell (MFC) is a bio-electrochemical device that harnesses the power of respiring microbes to convert organic matter in waste-water directly into electrical energy. At its core, the MFC is a fuel cell, which transforms chemical energy into electricity using oxidation-reduction reactions. The key difference is that MFCs rely on living biocatalysts to facilitate the movement of electrons throughout their systems instead of the traditional chemically catalysed oxidation of a substrate at the anode and reduction at the cathode. In this field the term substrate is used to describe a substance on which the microorganism acts to produce a chemical reaction, in this case organic matter contained in waste-water, usually in dissolved form.

The process behind MFCs is cellular respiration. Nature has been taking organic matter substrates and converting them into energy for billions of years. Cellular respiration is a collection of metabolic reactions that cells use to convert nutrients into adenosine triphosphate (ATP), which fuels cellular activity. The overall reaction can be considered an exothermic redox reaction.

In order for a fuel cell to work a complete circuit is needed. In the case of the MFC the cathode and an anode are separated by a cation selective membrane and linked together with an external conductor through the load. When an organic "fuel" is fed into the anode chamber, the bacteria oxidise and reduce the organic matter to generate the life sustaining ATP that fuels their cellular machinery. Protons, electrons, and carbon dioxide are produced as byproducts, with the anode serving as the electron acceptor in the bacteria's electron transport chain.

The electrons pass from the anode to the cathode through the external load connection. At the same time protons pass freely into the cathode chamber through the proton exchange membrane separating the two chambers. Finally oxygen present at the cathode recombines with hydrogen and the electrons from the cathode to produce water, completing the reaction.

The use of biological organisms responsible for catalysing electrochemical reactions, gives these systems a level of complexity that is perhaps above that of already complex electrochemical systems (e.g. batteries, fuel cells and supercapacitors). The main differences of MFCs to the conventional low temperature fuel cells are:

• The electrocatalyst is biotic (electroactive bacteria or proteins) at the anode.

• The temperature can range between 15 and 45°C, with close to ambient levels as optimum.

• Neutral pH working conditions.

• Utilisation of complex biomass (often different types of waste or effluent) as anodic substrate.

• A promising moderate environmental impact assessed through life cycle analysis.

MFC construction

A MFC consists of an anode and a cathode separated by a cation specific membrane. Microbes at the anode oxidise the organic substrate, generating protor.s which pass through the membrane to the cathode, and electrons which pass through the anode to an external circuit to generate a current. The problem is collecting the electrons released by bacteria as they respire. This leads to two types of MFCs: mediator and mediatorless. The mediatorless MFC is the most promising and is the main version used in developments. There are two basic versions of the MFC, the two cell and the single cell.

Two Cell MFC

This is illustrated in (Fig. 5.37 (a)). The cell consists of two compartments, containing the anode and cathode, separated by a permeable membrane. The anode cell contains the substrate (wastewater or organic material) and the anode, which is coated with a surface film of microorganisms. The cathode cell contains the cathode and the electrolyte. Substrate is fed to the anode cell and oxygen to the cathode cell. The anode cell is maintained in and anaerobic state i.e. is kept free of oxygen.

Single Compartment MFC

The single compartment uses an external air cathode which is separated from the inside of the cell by the membrane (Fig. 5.37 (b)). The air cathode version gives a higher power density than the two chamber version. In practice the MFCs are coupled together in stacks to provide the required voltage.

MFC_S and Waste-Water Treatment

All types of waste-water containing organic matter can be treated by this process, including domestic waste-water, brewery effluent, and much else. Several plants are in operation and have shown good results. Use of MFCs for waste-water requires a design which allows the waste-water to flow through the cell over the anode surface. Various configurations have been adopted for this purpose, including the tubular MFC where the cathode is placed on the outside of the tube and the anode occupies the full internal space. Waste-water flows through the anode from one end to the other.

MFC reactions

The mechanism of oxidation and reduction in the MFC is not clearly understood, and various reactions have been proposed to explain the process. An example using acetate as the substrate follows: