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A growing population, urbanization and an increase in the number of industries is causing an increase in sewage sludge (SS) that needs to be either beneficially used or disposed of. Application of SS to agricultural lands is a well-known practice but the plant available phosphate and phosphate fertilizer value of SS has been of concern. This is especially due to the wide variety of soils that SS is applied to and the different phosphate removal processes that sewage waste water undergoes at the water care works and the source used to produce SS. Phosphate phyto-availability and phosphate fertilizer value of petrochemical and municipal wastewater sludges (SS) were determined in four different soils using an incubation study over 168 days, a pot trial over 42 days and a field trial over one season. Phosphate phyto-availability was determined/calculated by means of an incubation approach. Soils were incubated with sludge as well as mono ammonium phosphate (MAP). The soils were then subjected to a Bray-1 extraction after a certain time (42 days, 168 days). The relative phosphate fertilizer value (RPFV) was then expressed as a percentage of the Bray-1 extractability of the sludge-amended soil, relative to the MAP-amended soil. The influence of soil properties, especially clay content, and sludge properties namely phosphate extraction method (chemical and biological) from waste water stream, was investigated to determine the effect on phytoavailability and fertilizer value of phosphate in SS-amended soil. Soil properties were the dominant factor determining plant available phosphate, where plant available phosphate decreased with increasing clay content, irrelevant of the type of treatment. There were, however, significant differences between the chemical and biologically removed SS, where the biologically removed SS had higher plant available phosphate. The RPFV % of the SS was comparable to MAP in terms of its plant availability. Wetting and drying cycles in the pot trial influenced the plant available phosphate from the SS, where the chemically treated sludge showed in general lower plant availability. The RPFV % of the biologically removed phosphate sludges was better than that of MAP and that of the chemically phosphate removed sludge were lower. Application of all the different sludge types resulted in a positive reaction on plant available phosphate for all the soils. All the trials were conducted at pH of about 5.5. However, it is expected that biologically P removed sludge will perform better in acid soils. The reason being that ferric phosphate in the chemically treated sludge is less soluble under pH conditions lower than 5.5 than above it. / Dissertation (MScAgric)--University of Pretoria, 2014. / tm2015 / Plant Production and Soil Science / MScAgric / Unrestricted

Denna rapport presenterar resultat och analys av prestandan i ett pilotförsök om temperaturstegsrötning (TPAD). Pilotförsöket genomfördes på uppdrag av Käppalaförbundet. Resultaten jämfördes med en nedskalad mesofil process som simulerade den nuvarande fullskaliga rötningsprocessen på Käppala  avloppsreningsverk. Syftet var att utvärdera om TPAD kunde erbjuda fördelar jämfört med det mesofila systemet. TPAD har tidigare visat stor potential i pilotstudier och till viss del i fullskaliga implementeringar på avloppsreningsverk runt om i världen. Då prestanda och beteende vid rötningsprocesser dock är starkt beroende av lokal slamkomposition och processparametrar, behövdes en skräddarsydd pilotstudie för att utvärdera TPADs applicerbarhet vid Käppala avloppsreningsverk specifikt. Sammanfattningsvis visade TPAD något bättre metanutbyte än det mesofila kontollförsöket (MAD), och VSD ökade markant. Dessa fördelar erhölls trots den lägre totala retentionstiden för TPAD. Kvävemineraliseringen ökade dock också märkbart vilket potentiellt kan medföra ökade kostnader associerade med rening av kväve i rejektvattnet för avloppsreningsverket. Avvattningsprov på labbskala visade ett omfattande utsläpp av TSS i rejektvattnet efter det termofila rötningssteget. Detta förbättrades dock avsevärt (om än inte i samma utsträckning som MAD) efter det mesofila skedet. Mycket preliminära resultat indikerade att TPAD hade en utmärkt inneboende hygieniseringsförmåga tack vare det termofila skedet, och resulterade i ett slutgiltigt rötslam som uppfyllde hygieniseringsriktlinjer enligt Revaq. TPAD verkade uppvisa hög robusthet, utan någon uppenbar syrakollaps trots hög belastning i det termofila steget. Framtida stresstester föreslås för att tvinga fram en termofil syrakollaps, vilket skulle kunna ge en syra/gas-fasad TPAD, med potentiellt ytterligare ökad prestanda enligt mycket av den befintliga litteraturen. / This report analyzes the performance of a pilot scale temperature phased anaerobic digestion process (TPAD) undertaken on commission from the Käppalaförbundet wastewater treatment plant. Results from the newly initiated TPAD pilot were compared to those of a scaled down mesophilic process simulating the current full scale digestion used at Käppala, to evaluate whether TPAD could provide benefits over the mesophilic system. TPAD had previously showed great promise at pilot and full scale at other plants around the world, but given that anaerobic digestion performance and behavior are highly dependent on local sludge composition and process parameters, a bespoke pilot was needed to evaluate TPAD at Käppala WWTP specifically. In summary, the TPAD exhibited slightly better methane yields than the mesophilic control, and showed better removal of volatile solids. Such benefits were seen despite the lower overall retention time of the TPAD. Nitrogen mineralisation however also increased, potentially imposing increased costs associated with sludge liquor nitrogen purification. Dewaterability tests showed the thermophilic stage of TPAD releasing large amounts of problematic colloidal material, which however was reduced by the subsequent mesophilic stage. Preliminary results indicated the TPAD had an excellent inherent hygienization ability owing to the thermophilic stage, producing a final digestate which fulfilled Revaq hygienization guidelines. The TPAD also seemed to exhibit great robustness, with no acid collapse in the thermophilic stage apparent despite high loads and short retention times. Future stress tests are proposed to test an acid-gas phased TPAD, with potentially further increased performance as per much of the existing literature.