Hi I work for Waste Solution's of New Zealand. Some may know us from the biogas vehcle work in the 1970's at Invermay. We design anaerobic digestion systems, usually large scale. Mostly we are doing lagoon based systems but we also do tank based. The systems we do are specifically designed for each site but they have recycles, hydraulic and induced gas mixing and baffle systems etc.. We are told by our clients in South East Asia that for Starch, ethanol and POME wastewaters they are about 40% lower cost than the tank based systems. Because of the very long SRT we get a better methane yield and a reduced residue mass. We do find that the methane percentage is lower as most tank systems have some form of pre-fermentation which sheds some CO2 prior to the gas capture. There are others that do similar type of lagoon systems. Equally there are a lot of people doing very simple lagoon based systems that are really just a hole in the ground with a cover an inlet pipe and two outlets (Gas and effluent). Because of the advanced pond reputation these are sometimes being sold for much more than is justified but often fail after a year or two. However, they have their place as long as the user is aware of the issues and pays a fair price. There is really a wide range of lagoon design forms. Make sure you know what you are getting .
We are about to start detailed design for an agricultural based factory processing about 1000 tonne per day sold residue in the UK. Extensive lab and pilot scale work has demonstrated that the engineered lagoon system gets a better methane yield and more importantly the digestate is much more amenable to dewatering due to a lack of gels etc. Without polyelectrolyte dosing the lagoon based system achieves a dry solids content after centrifugation of 30% compared to 12-14% for anaerobic contact systems (CSTR plus solids capture and recycle). The liquor left from dewatering is recycled. A bleed stream passes to polishing treatment shared with low COD wastewaters from the factory. Thus the lagoon system needs much less further processing than the equivalent tank based system. The lagoon uses more land and requires more heat but its waste heat leftover form existing heat recovery in the factory complex. The lagoon is simpler to operate and less prone to inhibition due to its size. Our client took a long time to make the decision between reactor types but for this specific case the lagoon gives a better solution. Stage 1 is 100,000 Nm3 CH4/day. Because of site issues the lagoon construction is much more expensive than usual to the extent that lower cost was not a driver for this plant. This is not advertising, we are too busy to do more projects for the foreseeable future. I normally don't comment much due to the commercial nature of our business and the resistance to such in this forum. But I wanted to show that there is a range of lagoon based options out there with a wide range of flexibility to suit most situations. One advantage is that even for the more advanced systems such as ours they are mechanically simple and easy to operate. The operators don't need experience and get about 2 weeks training. Equally tank based systems have there place especially where land is limited or in high demand. Based on our experience all AD systems will need some form of polishing treatment. What hasn't been mentioned is that most European AD system are designed predominantly to reduce labour requirements as that is generally expensive there. Net energy yield and final degree of treatment seem to mostly be a distant second. Note that a number of these systems quote the overall removal efficiency but that includes the pre-treatment and secondary treatment which do not produce gas and also omit the sludge wasting COD as well. There are a huge number of anaerobic digestion systems in the market place. Each has advantages and disadvantages. Each haws it's place and we get successful outcomes when the reactor type is most suited to the task and surrounding issues. In reality we find that the biology is pretty simple it's the materials handling issues that result in downfalls. Too many people use water pumps and other equipment that is either not suitable for the wastes or cannot be maintained with the local resources. We did one small system onto a Pacific Island. The mixing was inefficient simply because the more efficient forms of mixing equipment could not be supported. Regards Chris Hearn CPG New Zealand Ltd T +64 3 470 7814 | F +64 3 479 2249 | M +64 21 912 096 Level 1, John Wickliffe House, 265-269 Princes Street, PO Box 910, Dunedin 9054, New Zealand cpg-global.com<http://www.cpg-global.com> P Please consider the environment before printing this e-mail. The information contained in this email communication may be confidential. You should only disclose, re-transmit, copy, distribute, act in reliance on or commercialise the information if you are authorised to do so. Any views expressed in this email communication are those of the individual sender, except where the sender specifically states them to be the views of CPG New Zealand Ltd. CPG New Zealand Ltd does not represent, warrant or guarantee that the integrity of this communication has been maintained nor that the communication is free of errors, virus or interference. From: [email protected] [mailto:[email protected]] On Behalf Of Paul Harris Sent: Monday, 6 December 2010 1:20 p.m. To: 'For Discussion of Anaerobic Digestion' Subject: Re: [Digestion] High costs of biogass plants in Norway G'day All, Please try to accept peoples personal opinions without attacking the person. If the opinion appears wrong to you leave individuals out and explain your own point of view, please. In my opinion anaerobic digesters are just part of a waste treatment system that may also generate energy and organic fertiliser. The type of digester needs to be selected keeping in mind the expertise and situation/climate in which the digester will operate. With this in mind the digesters suitable for Europe (and North America?) will probably not be suitable for most situations in Australia (where we have LOTS of space and technical support may be a long distance away) and definitely not for some of the less developed tropical countries. That said why should the less developed countries (who need, not want, energy more than Europe and USA) be deprived of the benefits of AD, where some treatment is better than none, because they don't meet "our" standards? We are all trying to learn, but I think one of the reasons AD is not greatly accepted/adopted in Australia is the perceived complexity/cost. Happy digesting, HOOROO Mr. Paul Harris, Room S116b, Waite Main Building Faculty of Sciences, The University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph : +61 8 8303 7880 Fax : +61 8 8303 4386 mailto:[email protected] http://www.adelaide.edu.au/directory/paul.harris CRICOS Provider Number 00123M This email message is intended only for the addressee(s) and contains information that may be confidential and/or copyright. If you are not the intended recipient please notify the sender by reply email and immediately delete this email. Use, disclosure or reproduction of this email by anyone other than the intended recipient(s) is strictly prohibited. No representation is made that this email or any attachments are free of viruses. Virus scanning is recommended and is the responsibility of the recipient.
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