Does energy matter?

Many of my posts are looking at how the energy efficiency of wastewater treatment can be improved. In fact one of my first posts was looking at exactly this. At large municipal wastewater treatment works that are constantly treating the waste produced by whole towns any little piece of energy they can save will help them cut costs. If we really could reduce energy usage down to zero for wastewater treatment, what sort of effect would that have on a country like Germany?

Energy usage by industry in Germany, 2014

So the energy usage of wastewater treatment is part of “Other” in the above chart. How much of “Other” is it?

Energy usage for wastewater treatment in Germany

You see that little red strip up there? That is total energy usage of all wastewater treatment plants in Germany when compared to other industries. Although only a small blip on the chart I have shown it adds up to one of the larger energy consumers for municipalities. This is all good, but what if we start looking at industry and some of the bigger pieces of the pie?

One interesting idea is to treat the highly concentrated wastewater from certain industries on-site. This makes the job of the municipal wastewater treatment works easier and should help reduce fees for wastewater disposal required by the factory. Some places where this makes sense include: paper production, milk processing, meat processing and abattoirs, and many food and beverage production facilities. The processes produce waste streams with very high organic loading, that can often be treated using anaerobic digestion.

A big advantage of anaerobic digestion that often gets touted is its ability to produce biogas as a potential energy source. This should make it super attractive to industries that need a system for treating their waste, right?

Well… Maybe. The big factor that comes into play is cost. Let’s say we are living in a perfect world where the treatment plant is running and most of the cost has been offset by the fewer waste disposal fees the factory now has to pay. What about all that biogas being produced? How much of an effect would the energy recovered from biogas production have on a large factory? Let’s have a look at energy costs for industrial use in Germany for an example week, the blue line below is the continuous average price of energy in €/MWh.

Source: https://www.energy-charts.de/power_de.htm
Source: https://www.energy-charts.de/power_de.htm

What the hell is happening at the end there?!?! The actual price of energy is negative, people are paying me to use more energy now or what? Yes, actually. Even if you ignore the negative prices (the phenomenen for which the priority given to renewable energy is often blamed) it is possible to see the change in energy prices even within a single day. If you are running a large factory and someone says you can save so and so much money by building a biogas plant and processing your waste into renewable energy and someone else comes and says you can save even more money by just running one of your production lines a bit later in the evening, which option do you choose?

So at the moment energy does matter but money matters more.

Industry 4.0 & Water 4.0

‘Industrie 4.0’ is a term that originated in Germany around 2011. It describes the next generation of industrial production based on cyber-physical systems. The National Science Foundation defines a cyber-physical system as:

…the tight conjoining of and coordination between computational and physical resources.  We envision that the cyber-physical systems of tomorrow will far exceed those of today in terms of adaptability, autonomy, efficiency, functionality, reliability, safety, and usability.

NSF 10-515 

The closest thing to ‘Industrie 4.0’ in English has been suggested to be ‘The Internet of Things (IoT)’, which I feel isn’t correct as Industry 4.0 is really, as the name suggests, focused on industry.

So why 4.0? The idea is that we have already had 3 industrial revolutions. The first was the introduction of mechanical production systems powered by water and steam, such as the automatic loom. The second is when electrically powered assembly lines appeared, massively increasing production output. The third was the implementation of electronics and information technology into the production industry through the use of devices such as the programmable logic controller or PLC. As to why they say 4.0 instead of just 4 or 4th, I’m just guessing it sounds more modern and computery. Atleast they didn’t call it ‘iRevolution 4.0’…

 

industry-4-2

So now Germany wants to bring this same idea to the water industry with the inventive name ‘Wasser 4.0’. Now we have a problem here, as recently a book was published in America called ‘Water 4.0’. Professor Sedlak already describes his 4 revolutions in the water industry in this book. Water 1.0 is the distribution of water in ancient Rome using pipes and canals. Water 2.0 is the treating of drinking water using filtration and chlorination. Water 3.0 is the development of wastewater treatment plants and sewage networks. This leads to his concept of Water 4.0 regarding technologies to deal with water shortages.

I think this is different to what the Germans wish to convey when they speak about ‘Water 4.0’. Water 4.0 is the same as Industry 4.0 but applied to the water industry, that is the digitalisation and networking of automation and monitoring systems and the introduction of smart technologies in water and wastewater treatment. In this example there aren’t any water 1.0’s or 2.0’s as Water 4.0 is just a copy of Industry 4.0 but for water.

However, I think there could be an image for Water 4.0 that describes the revolutions in the water industry over the past century in a simplified way. In this concept I would say the first water industry revolution was the usage of chemicals and sedimentation in the treatment of water and wastewater. The second revolution was the discovery of the activated sludge process for wastewater treatment in the UK at the beginning of the 20th century. The third revolution was the implementation of membranes for desalination and wastewater treatment and recycling. The fourth revolution then matches up with that of ‘Industry 4.0’ with the implementation of advanced cyber-physical systems.

 

water-4

In the end, it will probably be another 100 years before we can really look back and say “That was when the 4th revolution occured in the water and wastewater industry”. At the moment it is still difficult to say what these 4.0 revolutions in industry and in water are even going to mean? Are we going to see a big increase in production and capability suddenly? Will everything be automated and everyone out of a job? Is there going to be a big adjustment where we enter a new golden (or dark) age or is it going to be just another little blip in history where there was lots of talk but not much really changed… Only time will tell.

 

 

 

Treatment or Recovery

There has been a trend in recent years for renaming some standard terms in the wastewater industry. Wastewater Treatment Plants (WWTP) are now being increasingly called Wastewater Recovery Plants (WWRP) and wastewater sludge should be referred to as biosolids for example. Some wish to actually change the name of wastewater itself!

So why is this happening?

Well, the most interesting components in typical municipal wastewater (we will keep calling it that for now) are the organics, which we will measure using the term chemical oxygen demand (COD) or how much oxygen is needed to remove them, ammonium and phosphate. We want to prevent these components from getting into our rivers and streams. But if instead of just looking at how to get rid of them, we look at how we might be able to extract and use them, we start to see how the term recovery can be used instead of just treatment.

So why are these components worth recovering?

The COD can straight away be converted into useable energy as biogas and ammonium and phosphate are important for fertilizers.

A term that was exciting a few years ago but seems to have dropped off most peoples radar at the same time they forgot about the whole ‘peak oil’ thing was ‘peak phosphorus’.

Looking at the above graph it is interesting to see that although there is a downward trend in searches for ‘peak phosphorus’, the large peaks in interest were followed by chunks of noone searching in the first few years after 2004 while more recently there seems to be a more sustained albeit lower interest.

I hope that this means there are still people keeping an eye on the ‘disappearing nutrient’. In the wastewater industry there are definitely people looking at all sorts of ways of recovering the phosphorus we are flushing down our toilets. Things like ion exchangers, membranes, electrochemistry and algae are all being investigated as possible methods for recovery.

I personally like the idea of capturing the phosphorus and nitrogen in algae. This algae can then be directly used as a fertilizer on crops. But then we don’t call it fertilizer anymore, we call it Biofertilizer…

 

 

Wastewater treatment sans oxygen

Anaerobic digestion is the term used to describe the treatment of wastewater in an oxygen free environment. Normally, municipal wastewater is treated with microorganisms mixed through the liquid with lots of air (so aerobic treatment). The oxygen provides lots of energy for the organisms to grow and quickly consume nutrients in the waste, this prevents the nutrients from entering rivers and streams where they can cause all sorts of problems with the ecological balance of the environment. When consuming the same amount of nutrients, the total mass of microorganisms will be 10 times more when they have been provided with oxygen than not.

It is this huge mass of microorganisms combined with left over solids that is becoming an increasing problem in the developing world. They are treating more and more of their wastewater (which is good) using the same aerobic treatment systems that have been typical in the developed world for the last 100 years. These systems need lots of energy to pump oxygen into the waste and produce a huge amount of highly concentrated sludge that either just gets dumped into a landfill, which is just moving the problem around without really solving it, or incinerated.

Lots of research is now being dedicated to analysing the energy efficiency of treating the sludge using anaerobic digestion. But why are we making these systems more and more complicated? Lets look at the path the wastewater can take from when it first arrives at the treatment plant to when the different parts all exit the plant.

Steps in a typical wastewater treatment process

We are pumping energy into the wastewater (aeration) and then trying to remove it all again straight away in our sludge treatment step. Why do we add all that energy to our wastewater in the first place? Why not just remove the energy that is already contained in it and use it for something else?

Two problems. First, anaerobic digestion is slow. All that energy being pumped into the wastewater is being used to quickly remove the nutrients. If we aren’t pumping energy into our system in the form of oxygen the microorganisms need to just use the energy that is available in the wastewater and they grow and reproduce much more slowly. Second, the microorganisms currently being used in anaerobic digestion are not removing nitrogen from the wastewater. This is bad, because the nitrogen can be used by things like algae in our rivers and streams causing all sorts of problems

However, these two problems are being addressed. The slowness of anaerobic digestion can be improved by clever system design and control. By pumping the wastewater around the system very quickly and increasing mixing with the microorganisms great efficiency improvements can be seen, here the problem comes that more energy is needed to pump the wastewater around quickly and mix everything really well, so we are just putting more and more energy into the system again! Therefore, clever system design is required so that we can reduce both time and energy required for the treatment.

Regarding the second problem, at the end of the 90’s researchers at the Delft University in the Netherlands discovered a bacteria that can convert nitrogen in wastewater (in the form of ammonium and nitrite) into nitrogen gas without needing oxygen. This can mean huge energy savings and reduced greenhouse gas emissions. It could also mean a complete anaerobic wastewater treatment system that either requires much less energy than current wastewater treatment plants or, in the best case, a wastewater treatment plant that is actually producing energy from our waste rather than requiring more energy to treat it.

 

Energy in waste

A by-product of municipal wastewater treatment plants is a waste sludge. This sludge holds potential energy that we might be able to use. If we focus on Europe in this post we can look at the graph below to see how much wastewater is treated by different countries.

total_waste_treated_EU

We can then compare those numbers with the amount of biogas each country also produces.

total_biogas_EU

Germany is dominating here. However, most of this biogas is being produced by co-digesting energy crops, such as corn from viable farmland. Would it be possible to produce this much energy from the waste we produce anyway?

Let’s keep using Germany as an example. In 2013, Germany had a population of 80.6 million people. After treating all of their waste there was 1.8 million tonnes of sewage sludge remaining. If we read up on what the United Nations has to say on excreta and wastewater sludges we see that if we are being optimistic we can expect over 5kWh of energy per kg from this sludge just by burning it. That means by burning all the crap Germany is producing we have created 9 000 000 MWh or enough to power around 300 000 of their homes.

However, Germany’s sludge production is actually not as high as it might be due to many municipal wastewater treatment facilities treating the sludge in biogas plants before incineration, this reduces the amount of sludge by up to 50%. So let’s now look at how much energy they can pull out of the sludge in the form of methane before incinerating it.

An example biogas plant produces around 4 000 MWh per year of energy from wastewater sludge generated by a city with a population of approximately 100 000 people. So we have another 3 224 000 MWh per year of energy from biogas. That is another 100 000 homes!

Ok, so that only gets us to around 1 million tonnes of oil equivalent, which is well under what Germany is currently producing using energy crops. Also, all that energy is usually getting fed back into the plant used to treat the initial influent (part of the energy is used for heating the biogas plant, but a much greater amount is required for powering the initial treatment plants aeration systems). So actually we have no homes being powered by crap…

But new research is investigating how we can get rid of these aeration systems and treat all of the wastewater using robust and energy efficient variations of the biogas plant.

This might be a bit optimistic! But having wastewater treatment plants that are net energy producers rather than energy consumers could become a real possibility in the near future.