Friday, 10 August 2018

Why I am pulling 100% degradable plastic bags from my compost bin

My organic veg supplier has recently started using plastic bags with this logo on. It says they are '100% degradable'. Perhaps I was naive in assuming that meant it was OK to put the bags in the compost bin. It turns out that they are 'oxo-degradable', a technology which is highly controversial.  They are currently banned in France and Spain [1]. 150 organisations including the World Wildlife Fund, Unilever and British Plastics Federation Recycling Group have signed a statement calling for them to be banned completely [2]. Now the European Commission has called for all member countries to take measures against them [3].

Wednesday, 18 July 2018

Climate change is here - how do we adapt?

Like a lot of people I've been suffering in the hot weather recently as has my work (low productivity) and my partner (due to my grumpiness). June has been a record breaking scorcher for many people. In East Anglia the temperature is several degrees above average and we have had only 12% of the normal rain fall [1]. July so far has been at least as bad. Climate change is going to bring more of this and other weather extremes. We are not suffering as much as other parts of the world but we do not escape entirely. So what can we do?

[By the way I am organising a workshop on this topic: Adapting our homes for Climate Change on 15th October. This will be one of five events to go with this year's OpenEcoHomes house tours. If you have tips to share or would like some advice please put this in your diary.]

The problem weather we need to cope with includes heavy rain and floods as well as heatwaves and drought. As with energy efficiency, there are a whole range of measures we can take from very low cost (e.g. more ice cube trays in the freezer) to higher cost (blinds or solar control film for windows) and requiring little or lots of advance planning (planting trees, politely requesting that potholes in the road should be fixed). Here are some ideas. I am sure you will have lots more.

Saturday, 26 May 2018

Why is Cambridge University dragging its feet on divestment?

How much time does it take to change investment policy at a university? Why do Cambridge university students need to go on hunger strike and occupy university office buildings to pressure the university to action? Back in January last year, after a vociferous campaign by students and academics the soverign body of the university ruled that ‘none of the University’s Endowment Funds should be invested directly or indirectly in companies whose business is wholly or substantially concerned with the extraction of fossil fuels.’ They also required the university council to publish a report within twelve months to set out how this should be done. It actually took a bit longer than that but earlier this month a report was produced (5 Mb pdf) and the recommendations in it, while not earth shattering, are a step in the right direction. However, even this is apparently a step too fast because the council are unable to agree to adopt even those recommendations. These include:

  1. No investment in tar sands or thermal coal (? What other kind of coal is there?)
  2. Commitment to the principles of the UNPRI (United Nations Principles of Responsible Investment)
  3. 10% of the fund to be invested in dedicated environmental, social and governance (ESG) funds

Saturday, 10 March 2018

How much energy can you get from rain?

Researchers in China have created a hybrid solar panel that can also make electricity from rain [1]. This has obvious advantages, especially for regions where you get more rainfall in winter than in summer because it will help to even out generation through the year. But how much energy can you actually get from rain? How does it compare with solar energy - and is it worthwhile? Here is a back of the envelope calculation.

Sunday, 11 February 2018

Uncertainty about pollution from wood stoves

In my previous post on air pollution, especially fine particulates (PM2.5), in Cambridge I concentrated on traffic, hardly mentioning wood stoves  as a possible source. However, wood burning is cited as an important source of pollution in parts of London [1] so why not Cambridge? To be honest I steered clear of the issue because there is such a huge amount of uncertainty I felt unable to present any facts with confidence. The National Atmospheric Emissions Inventory (NAEI) estimates that 35% of PM2.5 in the air is from domestic wood burning[2] - or it could be 10 times less [3].

The issue is so uncertain that the government is running a call for evidence on the issue. This runs until 27th Feb.  In their call for evidence they say [4]:
  • Burning wet wood (i.e. not properly seasoned wood) generates at least twice the emissions from dry wood.
  • Estimates for the proportion of wood that is burnt wet range from 80% (from the wood industry) to 20% (from a survey by BEIS).
  • Estimates of how much wood is burnt in total range for 3 to 6 million tonnes per year
  • Burning on an open fire generates up to 10 times the emissions from a modern wood stove.

Wednesday, 7 February 2018

Where does air pollution in Cambridge come from?

Air pollution is a big problem for our health, especially very small particles known as PM2.5 (less than 2.5 micrometres in size) that penetrate deep into our lungs. PM2.5 is more closely linked to death rates than the other pollutants [1]. Diesel cars are blamed for a large proportion of air pollution in our cities. But are they the only problem or even the main problem? Traffic is the main source of nitrogen oxides (NOx) in our cities but for particulates the story is more complicated.

  • Most NOx pollution in cities comes from traffic, mainly from burning petrol or diesel (especially diesel).
  • NOx dissipates fairly quickly.
  • Particulates (especially PM2.5) are partly related to traffic (including chemical reactions with NOx) but there are other sources.
  • Particulates can waft around and travel for long distances. Most of the particulates pollution in Cambridge comes from outside the city.

What this means is that while reducing traffic in the city, especially diesel cars, will reduce NOx levels, they will have less of an impact on particulates. Tackling that requires action across the region, not just the city.

Thursday, 25 January 2018

Is waste incineration sensible, a health disaster or a white elephant?

Amey have submitted a planning application for an Energy from Waste plant at their waste handling facility in Waterbeach [1]. Is this a good thing or a bad thing? There are potential concerns about air pollution, carbon emissions and disincentive to reycle. But it will divert stuff from landfill and probably reduce GHG emissions overall.

The facility will process residual waste – the stuff that has come through the Mechanical Biological Treatment and not been picked out as valuable, and the stuff that was rejected from the dry recycling plant, plus construction and demolition waste. This waste would normally go to landfill.

The waste will be burnt in a furnace at 850°C to produce electricity and also heat; they hope to supply district heating for new developments in the area.

Amey's main EfW inputs and outputs [1, section 4]