TECHNICALLY SPEAKING Barnard’s great lesson
A prize-winning researcher has always been an inspiration to Frank Rogalla of Aqualia. Here he reveals how to get the best results from biological phosphorus removal
he winner of the Lee Kuan Yew Water Prize was announced in Singapore in March, James Barnard, internationally known for his innovations in sustainable, non-polluting water treatment. Barnard was the pioneer behind the invention of biological nutrient removal (BNR) technology, about 40 years ago.
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Barnard was largely responsible for the discovery and development of biological nutrient removal, starting with the first publications more than 35 years ago: Barnard JL, Cut P and N without chemicals, (1974), Water & Wastes Engineering, Part 1, 11(7), 33-36; Part 2, 11(8), 41-43). Initially, these articles were not accepted by the scientific community, represented by the IWPRC (now the International Water Association), at its biennial conference in Paris that year. They were contrary to the conventional wisdom of the time and senior academics would say: “I have read it and I don’t believe a word of it.” This is the sign of true invention, something not obvious even for the specialist – Barnard had to overcome many hurdles to demonstrate that his findings were true, but in the process he has become one of the most widely respected water technologists in the world. It shows the many crucial qualities of a perfect professional: patient, persistent, pedagogical, and powerfully persuasive.
Today, the technology developed by James Barnard, biological phosphorus removal (BPR), has come of age – after having been introduced with the treatment plants for the City of Johannesburg in 1974. There are a large number of plants in the world today and a great variety of basin configurations are used. Generally, excellent process performance can be achieved with the right feed conditions and the correct design and operation, but still there are issues not fully understood. This led to the perception that biological phosphorus removal is unreliable and unpredictable – as the late Professor Harremoes, recipient of the first Stockholm Water Prize, once quipped: “We design for BPR, we hope for the best, but in the end we prepare for the worst: chemical addition.”
Problems observed in Bio-P plants may include nitrates in the feed, excessive
Technology developed by Barnard has come of age in plants around the world
return activated sludge (RAS) recycle rates, secondary release of phosphorus, and toxicity. Some of these issues that still frustrate some designers and plant operators will be presented below. There are also many claims for excellent removal from plants that would appear not to conform to the well established principles for BPR, but when considering the full picture, explanations and ways to obtain predictable and reliable removal can be found by proper understanding of the process. To obtain phosphorus removal in activated sludge plants, Levin (1970) first proposed the Phostrip Process, subjecting the return activated sludge (RAS) to up to 30 hours of anaerobic conditions in a thickener (stripper). The resulting release of phosphorus could be treated with lime, decanting the supernatant containing excess phosphorus, and returning the underflow of the stripper to the aeration basin.
Milbury (1971) noted good phosphorus removal in a few high rate plants, but saw that
performance was lost when there were nitrates in the effluent. Similarly, Barnard (1974) noted that phosphorus removal only occurred in his pilot plant when effluent nitrate concentration was less than 4mg/l.
He had studied phosphorus removal in a
100m3/d pilot plant designed for nitrification and denitrification, and saw that phosphorus was released at the end of the anoxic zones and was taken up to low levels in the subsequent re-aeration zone. He found out that it was necessary for the RAS to pass through a zone free of nitrates and dissolved oxygen, in order for phosphorus to be released. From these observations developed an alphabet soup of processes, all with the same aim to reduce the nitrates in sludge returns and to allow the optimal use of the existing sources of readily biodegradable carbon compounds, necessary to favour the growth of phosphate accumulating organisms (PAO). These had been first identified by Fuhs and Chen (1975), proposing that some bacterial species,
April 2011 Water & Wastewater Treatment 39
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