Water reuse for agricultural irrigation can contribute to the conservation of valuable water resources and opens the possibility to reuse the wastewater's nutrients (N and P) at the same time. As irrigation is usually limited to vegetation periods, effluent requirements for treated wastewater may vary seasonally. A process concept for wastewater treatment with variable operation modes for the seasonal production of nutrient-rich irrigation water and nutrient-poor discharge water is proposed. It is shown that a two-step process consisting of organics removal followed by biological aerated filters (biofilters) for nitrogen removal is a promising combination which allows a flexible and seasonally varied operation with a fast re-start of biological nitrification after shut-down periods. To date, there is no commonly accepted practice amongst operators to take biofilters out of service for periods of time while - at the same time - maintaining biological activity to enable a quick start-up. This paper shows that during shut-down periods the activity drop rate is the smallest if the filter bed is maintained flooded and without aeration; then a very quick re-start is possible.
TIn 2004, the German Association for Wastewater, Water and Waste (DWA) carried out a survey about the current status of sewage sludge treatment and disposal in Germany. The study covered about one third of the wastewater treatment plants and about two thirds of the entire treatment capacity (expressed in population equivalents) in Germany. This provides an up-to-date and representative database. The paper presents the most important results regarding sludge treatment, process engineering, current disposal paths and sewage sludge quality.
Greywater is an excellent resource for service water in intra-urban reuse. By substituting fresh water with appropriately treated greywater, it is possible to save 30–50% of fresh water. In this paper, an up-flow pilot biological aerated filter (BAF) is tested for the treatment of synthetic greywater and the design parameters are determined. An organic load of 8 kg COD/(m3 d) allows to achieving a good effluent quality with regard to COD, suspended solids, and anionic surfactants. By reducing the organic load to 5 kg COD/(m3 d) full nitrification is achieved as well. A process set-up for a full-scale BAF greywater treatment plant is proposed and dimensioned using the parameters from the pilot plant tests. Here, the required specific volume is approx. 3 L/C for the reactor and 16 L/C for the storage tanks. This feature make the BAF a compact process which can be successfully integrated in intra-urban water reuse schemes.
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