Anaerobic Digestion Archives - Page 4 of 4 - Haigh Pipeliner Macerators

Anaerobic Digestion

Rising Food Waste Concerns – WRAP Report

Posted on September 6, 2021April 12, 2022 by Elliot Volpe

06
Sep

Food waste continues to be a major problem in the UK, as published in the WRAP food waste report. With so many outlets offering quick, easy and cheap food it often takes priority over using what we have in the cupboards. Or, when it doesn’t seem appealing to throw together some ingredients and make a nutritious meal, instead we opt for the easy, far less healthy option.

If there is one thing the pandemic has taught us (besides not needing to bulk buy toilet rolls) is that when there is threat of food shortages and fast-food outlets are closed, that we can in fact make do perfectly well with the necessities. This is proven by the fact that 79% of UK citizens undertook additional food management behaviours in 2020.

Food waste dropped dramatically in the first lockdown (by 43%) and remained well below pre-pandemic levels across all of 2020. Many people adopted the behaviours such as freezing/defrosting food, using up leftovers and batch cooking.

In the UK, 70% of food waste (post-farm gate) comes from households, equivalent to a value of over £14 billion. This equates to 20 million tonnes of greenhouse gas (GHG) emissions. With food waste levels replicating those seen back in 2018, it does raise concerns that people have shifted out of their pandemic mindsets and are well and truly back into old habits.

What Does the WRAP Food Waste Report Mean for AD?

Food waste isn’t a positive thing. If it can be consumed, then it should be. Nobody wants to see food being wasted, especially as most of the time it is perfectly good food. As far as AD is concerned, food waste can be used in the process.

It is certainly better for food waste to be brought to AD plants for processing, meaning that it plays a part in renewable energy production. Otherwise, food waste goes to landfill and becomes yet another pollutant of GHG in the atmosphere.

Yes, the more food waste coming to AD sites to be processed, means more money for the system providers, but a moral approach has to be considered here. Just because it will mean more money in back pockets, that does not mean it should be wholly supported.

If there is valid reason for the food waste, then it should be processed by an AD plant and turned into renewable energy. However, we should be looking at ways of dealing with this problem at its source. That is by educating people on how to change behaviours with regards to food management and waste. But, also educating them on the effects their food waste is having on the environment they live in.

Reference – WRAP Report

Anaerobic Digestion

Anaerobic Digestion: A Plants Location

Posted on September 3, 2021April 12, 2022 by Elliot Volpe

03
Sep

As Anaerobic Digestion became more popular from 2010 onwards, this meant the construction of Anaerobic Digestion plants became more appealing, even on a smaller scale.

Because of this, we now see Anaerobic Digestion plants situated across the UK. As the Feed in tariff started to phase out, we have seen less small-scale construction over the last few years.

However, there are different types of plants that are slowly becoming more viable, allowing to the right licenses, and ensuring that authority guidelines are followed.

The locations of small-scale Anaerobic Digestion plants are commonly on farms, as a way of utilising the waste and turning it into profit. Because of this, these small-scale plants lend themselves to wherever the farms are situated. Although, as part of the planning process, accessibility is one of the main focal points.

For larger scale plants, we often see a more centralised location that acts a “hub”. This centralised plant lends itself to waste collection companies and their profitable work of collecting waste from other people’s homes, often at a cost, and then putting it into their digesters. Then making money from the output of the system. Meaning this set up is a viable and healthy business opportunity.

Locals may opt to bring waste to the location, rather than having it collected. When this is done, they may be charged a gate fee. The idea of this is to allow the plant to receive payment for the disposal of someone else’s waste.

Larger scale Anaerobic Digestion plants cost more to construct and certainly take a lot of time and planning to be fully operational. This is why larger Anaerobic Digestion plants are not typically on farms or in gardens. They are often found on purpose-built sites, as it would be ineffective to construct a multi-million-pound plant on a site that is not fully able to cope with any aspect of the process.

Anaerobic Digestion

pH – It’s All About Balance

Posted on August 31, 2021April 12, 2022 by Elliot Volpe

31
Aug

The pH balance in the anaerobic digestion process is critical. If the pH level is unstable, it can lead to underwhelming biogas yields, and often leads to odour from the process. There is a sweet spot for the pH levels to enable sufficient yield.

In an experiment conducted on grass silage and its biogas yield, dependent on process variables, it showed there is desirable combinations in the systems. These optimum points are largely down to the temperature and pH levels in the digester.

A mesophilic process normally sees the temperature set between 30-38˚c. In this experiment in particular the temperature was set at 35˚c. The pH levels were tested at 3 different levels. These were: 6.5, 6.8 & 7.2

The established, best combination for a mesophilic process was a pH of 6.8 at 35˚c. This combination saw a biogas yield of over 60%.

Multiple pH levels and temperatures were then trialed to find the best overall yield. The highest yield from the experiment as a whole, was achieved from having a temperature of 45˚c, at a pH of 6.5. It is thought that the reason for this is that the pH levels and temperature allowed for rapid growth of the bacteria that produce the biogas.

Continuous monitoring of the pH level in the digester is essential. It can be the difference between producing high amounts of biogas or unsatisfactory amounts. Less gas produced, equates to a less profitable process.

Anaerobic Digestion

How to Achieve 23% More Biogas Yield

Posted on August 27, 2021April 12, 2022 by Elliot Volpe

27
Aug

Biogas yield is one of the main priorities in any Anaerobic digestion process. The more gas your digester can produce, the more gas you can use to generate electricity, or feed back into the grid. In short, more gas produced = more money made.

Sisal fibre was used in an experiment to explore the link between substrate degradation and biogas yield in a process. This was to see how the industry can get the most from their AD system.

The report shows that the sisal fibre degraded in the digester went from 31% to 70% in the experiment. Biogas yield from this particular experiment increased 23% m³ CH₄/kg.

How was this done? Maceration.

It has been proven that maceration of the feedstock can lead to quicker degradation of the substrate, in turn, producing a higher gas yield from the process. In this experiment, the original substrate used was raw and untreated. The substrate was then macerated to 2mm to see the difference in process outputs.

Of course, macerating feedstock to 2mm in an AD system may not always be practical. However, this experiment proves the importance of macerating feedstock to get the most out of your process.

Anaerobic Digestion

What Is Anaerobic Digestion?

Posted on August 13, 2021February 14, 2022 by Elliot Volpe

13
Aug

What Is Anaerobic Digestion?

The process of anaerobic digestion dates as far back as the 19^th century. The process itself has evolved over time from open lagoon systems, through to creation of closed tanks to get optimum yield from the process.

So, what is it? Anaerobic digestion is the breakdown of material in the absence of air. Feedstock is fed into the digester tanks and left to sit there at a set temperature. Over time the material goes through different stages and gets broken down by microorganisms, with the result being a methane rich biogas.

Once the reaction has taken place, the methane can then be used to power a combined heat and power (CHP) unit, which often is used to generate electricity to allow sites to be self-sufficient. Any unused electricity is sold back to the grid. Some sites take the methane and export it straight back into the grid as soon as it is extracted from the process.

As a bonus, the digestate that is left in the system once the reaction has occurred is a nutrient rich fertiliser, which farmers can then spread on their land.

How Does AD Cut Emissions?

Anaerobic digestion is a renewable energy system, as the feedstock can be replenished at no harm to the environment. Often, cow manure is used for the feedstock, which is the first stage of the process. Then, at the end of the process the nutrient rich digestate is then spread onto the fields in which the cows eat the grass from. This means it is seen as almost net zero carbon emissions, making it a popular choice in the drive for renewable and clean energy.

In some cases, food waste is used as a feedstock. This means that the food waste that would usually decompose and emit harmful gases into the atmosphere is now being used as the input to a system that can then be turned into energy.