Phosphorus bioavailability from land-applied biosolids in south-western Australia

The annual production of biosolids in the Perth region during the period of this study was approximately 13,800 t dry solids (DS), being supplied by three major wastewater treatment plants. Of this, 70% was typically used as a low-grade fertiliser in agriculture, representing an annual land use area of around 1,600 ha when spread between 5 and 7 t DS/ha. Loading rates of biosolids are typically based on the nitrogen (N) requirements of the crop to be grown, referred to as the N Limiting Biosolids Application Rate (NLBAR). A consequence of using the NLBAR to calculate loading rates is that phosphorus (P) is typically in excess of plant requirement. The resultant high loading rates of P are considered in the guidelines developed for the agricultural use of biosolids in Western Australia, but lack research data specific to local conditions and soil types. Regulatory changes throughout Australia and globally to protect the environment from wastewater pollution have created a need for more accountable and balanced nutrient data. Experiments presented in this thesis were undertaken to ascertain: the percentage relative effectiveness (RE) of biosolids as a source of plant available P compared with inorganic P fertiliser; loading rates to best supply P for optimum crop growth; P loading rates of risk to the environment; and the forms of P in local biosolids. Therefore, both the agronomic and environmental viewpoints were considered. Anaerobically digested and dewatered biosolids produced from Beenyup Wastewater Treatment Plant, Perth with a mean total P content of 2.97% dry weight basis (db) were used in a series of glasshouse, field and laboratory experiments. The biosolids were sequentially fractionated to identify the forms of P present and likewise in soil samples after applying biosolids or monocalcium phosphate (MCP).The biosolid P was predominantly inorganic (92%), and hence the organic fraction (8%) available for mineralisation at all times would be extremely low. The most common forms of biosolid P were water-soluble P and exchangeable inorganic P (66%), followed by bicarbonate extractable P (19%) and the remaining P as inorganic forms associated with Fe, Al and Ca (14%). Following the application of biosolids to a lateritic soil, the Fe and Al soil fractions sorbed large amounts of P, not unlike the distribution of P following the addition of MCP. Further investigation would be required to trace the cycling of biosolid P in the various soil pools. The growth response of wheat (Triticum aestivum L.) to increasing rates of biosolids and comparable rates of inorganic P as MCP, to a maximum of 150 mg P/kg soil was examined in the glasshouse. The percentage relative effectiveness (RE) of biosolids was calculated using fitted curve coefficients from the Mitscherlich equation: y = a (1-b exp–cx) for dry matter (DM) production and P uptake. The initial effectiveness of biosolid P was comparable to that of MCP with the percentage RE of biosolids averaging 106% for DM production of wheat shoots and 118% for shoot P uptake at 33 days after sowing (DAS) over three consecutive crops. The percentage residual value (RV) declined at similar rates for DM production in MCP and biosolids, decreasing to about 33% relative to freshly applied MCP in the second crop and to approximately 16% in the third crop. The effectiveness of biosolid P was reduced significantly compared with inorganic P when applied to a field site 80 km east of Perth (520 mm annual rainfall). An infertile lateritic podsolic soil, consistent with the glasshouse experiment and representative of a soil type typically used for the agricultural application of biosolids in Western Australia was used.Increasing rates of biosolids and comparable rates of triple superphosphate (TSP), to a maximum of 145 kg P/ha were applied to determine a P response curve. The percentage RE was calculated for seasonal DM production, final grain yield and P uptake in wheat followed by lupin (Lupinus angustifolius L.) rotation for the 2001 and 2002 growing seasons, respectively. In the first year of wheat, the RE for P uptake in biosolids compared with top-dressed TSP ranged from 33% to 55% over the season and by grain harvest was 67%. In the second year, and following incorporation with the disc plough at seeding, the RE for P uptake by lupins in biosolids averaged 79% over the growing season compared with top-dressed TSP, and by grain harvest the RE was 60%. The residual value (RV) of lupins at harvest in biosolids compared with freshly applied TSP was 47%. The non-uniform placement of biosolids (i.e. spatial heterogeneity) was primarily responsible for the decreased ability of plant roots to absorb P. The P was more effective where biosolids were finely dispersed throughout the soil, less so when roughly cultivated and least effective when placed on the soil surface without incorporation. The RE for grain harvest of wheat in the field decreased from 67% to 39% where biosolids were not incorporated (i.e. surface-applied). The RE could also be modified by factors such as soil moisture and N availability in the field, although it was possible to keep these variables constant in the glasshouse. Consequently, absolute values determined for the RE need to be treated judiciously. Calculations showed that typical loading rates of biosolids required to satisfy agronomic P requirements of wheat in Western Australia in the first season could vary from 0 to 8.1 t DS/ha, depending on soil factors such as the P Retention Index (PRI) and bicarbonate available P value.Loading rates of biosolids were inadequate for optimum P uptake by wheat at 5 t DS/ha (i.e. 145 kg P/ha) based on the NLBAR on high P sorbing soils with a low fertiliser history (i.e. PRI >15, Colwell bicarbonate extractable P 2 mm, and thus their was little relationship between soil bicarbonate extractable P and P uptake by plants in the field. The risk of P leaching in biosolids-amended soil was examined over a number of different soil types at comparable rates of P at 140 mg P/kg (as either biosolids or MCP) in a laboratory experiment. Given that biosolids are restricted on sites prone to water erosion, the study focussed on the movement of water-soluble P by leaching rather than by runoff of water-soluble P and particulate P. In general the percentage soluble reactive P recovered was lower in soils treated with biosolids than with MCP, as measured in leachate collected using a reverse soil leachate unit. This was particularly evident in acid washed sand with SRP measuring 14% for biosolids and 71% for MCP, respectively, although the differences were not as large in typical agricultural soils. Specific soil properties, such as the PRI, pH, organic carbon and reactive Fe content were negatively correlated to soluble reactive P in leachate and thus reduced the risk of P leaching in biosolids-amended soil.Conversely, the total P and bicarbonate extractable P status of the soils investigated were unreliable indicators as to the amount of P leached. On the basis of the experiments conducted, soils in Western Australia were categorised according to their ability to minimise P enrichment and provide P necessary for crop growth at loading rates determined by the NLBAR. Biosolids applied at the NLBAR to soils of PRI >2mL/g with reactive Fe >200 mg/kg were unlikely to necessitate P loading restrictions. Although specific to anaerobically digested biosolids cake applied to Western Australian soils, the results will be of relevance to any industry involved in the land application of biosolids, to prevent P contamination in water bodies and to make better use of P in crop production

The impact of soil and moisture on nitrogen mineralisation rates in biosolids

Nitrogen (N) based loading rates are commonly used to determine land application rates of biosolids, calculated to best target the agronomic N needs of the crop. The rate of N mineralisation following the amendment of soils with biosolids over a range of specific environmental conditions needs to be accurately quantified to prevent overloading the soil with N in excess of plant uptake. The N release characteristics of anaerobically digested dewatered biosolids cake (DBC), lime-amended biosolids (LAB) and alum sludge (AS), in comparison to urea as a source of readily available N, were investigated in a soil incubation study. The experimental design included two soil types and three moisture regimes (25%, 50% and 100% gravimetric water holding capacity (GWHC)). There was no significant effect of soil type on the proportion or rate of N mineralisation. Nitrogen mineralisation rate was greater for LAB and AS compared with DBC and lime amended biosolids which had been stockpiled (LABs) for 12 months.The rate of N mineralisation was also dependent on moisture and was generally greater at 50% GWHC compared to 25% GWHC, but at 100% GWHC losses of N were observed, especially from soil amended with LAB; this is attributed to denitrification. The proportion of mineralisable N (% organic N) at 50% GWHC was greater for LAB (72%) and AS (64%) in comparison with DBC (32%) and LABs (26%). These results are consistent with previous findings and demonstrate that the organic matter content of LAB and AS is of a lower stability than DBC and LABs. Plant available N in the first season following the land application of biosolids may be greater than current estimates of 20% and hence N mineralisation, volatilisation rate and denitrification losses for specific products under a range of environmental conditions needs further investigation

Differentiation of biosolids from animal faecal material using the 16s ribosomal RNA genetic markers of gastrointestinal anaerobic bacteria

Recombinant DNA techniques were evaluated for their usefulness in distinguishing biosolids from faecal material of cow, kangaroo and sheep. It involved PCR amplification using published priming sequences, and restriction site profiling of amplified DNA across the 16S rRNA gene of anaerobic gastrointestinal bacteria, Bacteroides spp and Bifidobacteria spp. Of the three Bacteroides spp primer pairs, two were useful for cow faecal material though at lower annealing temperatures were also applicable to biosolids and sheep faecal material. The third primer pair was specific only for biosolids. All three primer pairs were not able to PCR-amplify Bacteroides spp sequences in faecal material of kangaroo. Of the three Bifidobacteria spp primer pairs, one was useful for sheep faecal material though at lower annealing temperature was also applicable to biosolids and cow and kangaroo faecal material. The Bifidobacterium angulatum specific primer pair enabled the PCR detection of anaerobes only in biosolids and in faecal material of kangaroo. The third, a Bifidobacterium catenulatum specific primer pair was suitable for faecal material of cow and at lower annealing temperatures was also applicable to the sample from sheep. For some primer sets, PCR amplification alone could not differentiate biosolids from other faecal samples. However, this could be resolved by digesting amplified DNA with the appropriate restriction enzymes. Overall, our evaluations show that recombinant DNA techniques have the potential to distinguish biosolids from other sources of faecal material, including that from kangaroo

Biosolids: Black gold in Western Australia

Of the three major wastewater treatment plants in the capital city of Perth, Western Australia, two produce dewatered biosolids cake (DBC) and the third produces lime-amended biosolids (LAB). The total production of both DBC and LAB in the 2004/2005-year was approximately 20,000 tonnes dry solids (t DS) and is increasing at a growth rate of 4% yr-1. The demand for Perth's biosolids as a low-grade fertiliser has outweighed supply and has achieved an average of 94% beneficial use for the past four years. The use of biosolids in Western Australia is strictly regulated by the 'Western Australian Guidelines for Direct Land Application of Biosolids and Biosolids Products 2002' (DEP et al. 2002). The three major users of biosolids in Western Australia include agriculture, forestry and composting accounting for 74%, 5% and 17% of the total biosolids production, respectively. Within the agricultural sector, the application of DBC commenced in 1996, mostly to wheat and canola crops in a dryland farming system. Local farmers have often referred to the biosolids as 'black gold' due to improvement in their crop yield and income following application. In forestry, biosolids research was commenced in 1998 on a 17 year-old pine plantation on the Swan Coastal Plain. Tree growth has improved significantly following the application of biosolids compared with inorganic fertiliser application, with no detrimental impact on groundwater quality. The composting of biosolids with other materials for domestic use and bagging has been practiced for more than 17 years.This paper summarises the evolution and current use of biosolids in Western Australia and highlights the main research programs instigated by the Water Corporation to ensure that Perth's biosolids are used beneficially and safely in the environment. Research has concentrated mostly on plant and tree nutrient uptake, particularly nitrogen and phosphorus, heavy metals, composting of biosolids, flies and pathogens. Much of the research data has been collected within the Australian National Biosolids Research Project (NBRP)

Utilisation of cattle manure and inorganic fertiliser for food production in central Uganda

Cattle manure and inorganic fertiliser use in smallholder peri-urban crop-livestock farms in Uganda was investigated by conducting a survey of 40 farms in the central districts of Wakiso and Kampala. The results showed that the major benefits obtained from cattle manure application were increased yields (52.5 %) and low cost of manure purchase (37.5 %). The major problems associated with its use included weight and bulkiness (75 %), lack of labour (67.5 %), insufficient quantities (55 %), high transportation and application costs (37.5%), enhanced weed infestation (35 %), poor hygienic conditions (32.5 %) and lack of storage facilities to maintain quality attributes of manure (32.5 %). A large number of farmers supplemented the cattle manure with other animal manures, such as poultry (45 %), pig (38 %), goat (33 %) and rabbit (18 %) manures where available. The majority of farmers (95 %) never supplemented manure with inorganic fertiliser claiming that it was expensive in terms of purchase and transportation (90 %) and lack of capital to purchase the fertilisers (67.5 %). Farmers were aware of the benefits of using cattle manure as a source of fertiliser in their crop-livestock production system. However, the nutrient content of cattle manure was low (0.42-0.56 % total N), being attributed to poor handling, collection and storage of manure, insufficient fodder and poor livestock diet, which need better management to maximise nutrient recovery. There was little information available to farmers regarding optimum management and rates of fertiliser application (both inorganic and organic) to improve crop yields, which is required to improve food security and economic development in Uganda. Ugandan extension services should therefore make efforts to intensify education among farmers in relation to soil fertility management options. In addition, farmers should collect and store the manure properly and preferably in a covered pit to enhance manure quality. Effective manure handling and storage systems should be designed that reduce loss of nutrients after excretion and during composting. Farmers should explore the viability of community based manure collection initiatives at the farm level where manure transportation costs are shared and hence minimized

Monitoring of waterways for evidence of faecal contamination from biosolids using DNA techniques.

Increased nutrient levels in inland waterways have led to algal blooms and eutrophication in many agricultural regions. To ensure fertiliser inputs are managed more effectively, the source of contamination needs to be tracked and identified. Point sources could include inorganic fertilisers, livestock excreta, or more recently biosolids. The presence of faecal indicator microorganisms has been widely used to identify the presence of faeces, however, these methods cannot distinguish between human and animals samples. This study investigated PCR amplification as a molecular method to distinguish biosolids from livestock faeces of biosolids, cattle, sheep, poultry and kangaroo. This was achieved using published priming sequences and restriction site profiling of amplified DNA across the 16S rRNA gene of anaerobic gastrointestinal bacteria Bacteroides spp and Bifidobacteria spp. Preliminary investigation showed that of the three Bacteroides spp primer pairs investigated, two were useful for cow faecal material; though at lower annealing temperatures were also applicable to biosolids and sheep faecal material. The third primer pair was specific only for biosolids. All three primer pairs were unable to PCR-amplify Bacteroides spp sequences in faecal material of kangaroo. Of the three Bifidobacteria spp primer pairs, one was useful for sheep faecal material; though at lower annealing temperature was also applicable to biosolids and cow and kangaroo faecal material. The Bifidobacterium angulatum specific primer pair enabled the PCR detection of anaerobes only in biosolids and faecal material of kangaroo. The third, a Bifidobacterium catenulatum specific primer pair was suitable for faecal material of cow and at lower annealing temperatures was also applicable to the sample from sheep. Varying degrees of success were observed in faecal material from other animals. Generally, biosolids tested positive for Bacteroides and Bfidobacteria with all primers except for those specific for B. angulatum. For some primer sets, PCR amplification alone could not differentiate biosolids from other faecal samples. The serial dilution of water contaminated by a range of livestock excreta and biosolids is being examined further to enable the sensitivity of this method to be applied in the field

Land application of lime amended biosolids.

Increased nutrient levels in inland waterways have led to algal blooms and eutrophication in many agricultural regions. To ensure fertiliser inputs are managed more effectively, the source of contamination needs to be tracked and identified. Point sources could include inorganic fertilisers, livestock excreta, or more recently biosolids. The presence of faecal indicator microorganisms has been widely used to identify the presence of faeces, however, these methods cannot distinguish between human and animals samples. This study investigated PCR amplification as a molecular method to distinguish biosolids from livestock faeces of biosolids, cattle, sheep, poultry and kangaroo. This was achieved using published priming sequences and restriction site profiling of amplified DNA across the 16S rRNA gene of anaerobic gastrointestinal bacteria Bacteroides spp and Bifidobacteria spp. Preliminary investigation showed that of the three Bacteroides spp primer pairs investigated, two were useful for cow faecal material; though at lower annealing temperatures were also applicable to biosolids and sheep faecal material. The third primer pair was specific only for biosolids. All three primer pairs were unable to PCR-amplify Bacteroides spp sequences in faecal material of kangaroo. Of the three Bifidobacteria spp primer pairs, one was useful for sheep faecal material; though at lower annealing temperature was also applicable to biosolids and cow and kangaroo faecal material. The Bifidobacterium angulatum specific primer pair enabled the PCR detection of anaerobes only in biosolids and faecal material of kangaroo. The third, a Bifidobacterium catenulatum specific primer pair was suitable for faecal material of cow and at lower annealing temperatures was also applicable to the sample from sheep. Varying degrees of success were observed in faecal material from other animals. Generally, biosolids tested positive for Bacteroides and Bfidobacteria with all primers except for those specific for B. angulatum. For some primer sets, PCR amplification alone could not differentiate biosolids from other faecal samples. The serial dilution of water contaminated by a range of livestock excreta and biosolids is being examined further to enable the sensitivity of this method to be applied in the field.Soil acidification is an increasing problem throughout many agricultural regions in Australia typically on lighter-textured soils that have a low buffering capacity to changes in soil pH and/or that may be naturally acidic. Crops and pastures grown on acidic soils are subject to problems such as aluminium toxicity (particularly in the subsoil), nodulation failure in legumes and a reduced availability of some nutrients. Lime and dolomite are products that are commonly applied to neutralise soil acidity and improve plant productivity with application rates often determined by their neutralising value and particle size of the product, and the pH buffering capacity (lime requirement) of the soil. To investigate the effect of lime amended biosolids (LAB) as a product for neutralising soil acidity and for improving crop growth, four rates of LAB (0, 5, 10 and 15 t DS/ha) and four equivalent rates of lime product (0, 2.3, 4.6 and 6.7 t/ha) were applied to an acidic red/brown sandy loam in the central wheatbelt of Western Australia. In addition, one rate of dewatered biosolids cake (DBC) at 7 t DS/ha was included to enable comparison to be made to this product. The experiment was conducted over three years and sown to wheat (Triticum aestivum), canola (Brassica napus) and then wheat in 2005, 2006 and 2007, respectively. Plants were sampled at 8 weeks and at harvest to determine the effect of LAB, lime and DBC on crop growth, nutrient uptake and grain yield. Samples of surface soil (0-10 cm) were collected and analysed at harvest for pH and major nutrients. Soil pH increased significantly with increasing rates of LAB or lime at the end of the first year, with similar values recorded between equivalent values of lime product. There was no significant change in soil pH following the addition of the DBC treatment. No further changes in soil pH had occurred by the end of the second year. The growth of both wheat and canola in the first two years was affected to a greater extent by nutrients (typically nitrogen) in the LAB than by the reduction in soil acidity. Measurements on wheat yield in the third year of the experiment and changes in soil pH in the surface (0-10 cm) and subsoil (10-20 cm) will provide further information as to the long term effects of LAB in agriculture and allow recommendations to be made regarding best practise land application rates

Decay of human enteric pathogens in agricultural soil amended with biosolids: Key findings from a comprehensive research project to examine potential health risks.

A comprehensive study was undertaken to examine the survival potential of enteric microorganisms in biosolids-amended soil, wheat plant phyllosphere, and stored grains. The presence of these microorganisms in the dust at harvesting time was also evaluated. In situ field experiments were conducted to examine the decay of E. coli (indicator bacteria), Salmonella enterica, bacteriophage MS2 and human adenovirus in biosolids-amended soils and in dust generated during harvesting of wheat. Glasshouse experiments were conducted to determine the survival potential of enteric microorganisms in the wheat phyllosphere and stored grains to determine any possible risks to humans or livestock through consumption of contaminated grains or fodder. The results of this study suggest that the target microorganisms decayed faster in the biosolids-amended soil compared with the unamended soil in the field, that the decay times were specific to the microorganism type; and that microorganism decay was correlated to declining soil moisture levels and increasing soil temperature. The risk of transmission of disease-causing microorganisms (human pathogens) from cereal crops fertilised with biosolids was considered to be low

Decay of Escherichia Coli in Biosolids Applied to Agricultural Soil

There is little scientific data available on the survival patterns of pathogenic microorganisms introduced into the soil through the broad acre application of biosolids. This study was conducted to investigate the decay rates of Escherichia coli in agricultural soil amended with biosolids during two different growing seasons in a dry temperature cropping region in Western Australia.Biosolids-amended and unamended soil were inoculated with E. coli (ACM 1803), inserted into sentinel chambers and placed into the topsoil (0-10 cm) of a wheat crop. Biosolids were applied to designated biosolids plots, according to normal district practice, and E. coli numbers within the sentinel chambers were monitored over time. E. coli numbers in biosolids-amended soil reached detection limits (>10 cfu/mL) within 6 to 7 months. The decay patterns of E. coli, by treatment difference (biosolids-amended or unamended), linear and quadratic relationships of sampling time, and their interactions were highly significant. The T90 or time taken for a 90% reduction in numbers in the biosolids-amended soil was estimated to be 74, 143, 183 days (2006) and 173, 211 days (2008) as compared with 188 days (2006) and 156, 242 days (2008) in the unamended soil. This research provides scientific data on the survival times of E. coli in agricultural soil, with and without biosolids and can thus be helpful to public health policy

Land application of sewage sludge (biosolids) in Australia: risks to the environment and food crops

Australia is a large exporter of agricultural products, with producers responsible for a range of quality assurance programs to ensure that food crops are free from various contaminants of detriment to human health. Large volumes of treated sewage sludge (biosolids), although low by world standards, are increasingly being recycled to land, primarily to replace plant nutrients and to improve soil properties; they are used in agriculture, forestry, and composted. The Australian National Biosolids Research Program (NBRP) has linked researchers to a collective goal to investigate nutrients and benchmark safe concentrations of metals nationally using a common methodology, with various other research programs conducted in a number of states specific to regional problems and priorities. The use of biosolids in Australia is strictly regulated by state guidelines, some of which are under review following recent research outcomes. Communication and research between the water industry, regulators and researchers specific to the regulation of biosolids is further enhanced by the Australian and New Zealand Biosolids Partnership (ANZBP).This paper summarises the major issues and constraints related to biosolids use in Australia using specific case examples from Western Australia, a member of the Australian NBRP, and highlights several research projects conducted over the last decade to ensure that biosolids are used beneficially and safely in the environment. Attention is given to research relating to plant nutrient uptake, particularly nitrogen and phosphorus (including that of reduced phosphorus uptake in alum sludge-amended soil); the risk of heavy metal uptake by plants, specifically cadmium, copper and zinc; the risk of pathogen contamination in soil and grain products; change to soil pH (particularly following lime-amended biosolids); and the monitoring of faecal contamination by biosolids in waterbodies using DNA techniques. Examples of products that are currently produced in Western Australia from sewage sludge include mesophilic anaerobically digested and dewatered biosolids cake, lime-amended biosolids, alum sludge and compost