T. W. Payn

Technological options for the management of biosolids.

Background, aim, and scopeLarge quantities of biosolids (sewage sludge), which are produced from municipal wastewater treatment, are ever-increasing because of the commissioning of new treatment plants and continuous upgrades of the existing facilities. A large proportion of biosolids are currently landfilled. With increasing pressure from regulators and the general public, landfilling of biosolids is being phased out in many countries because of potential secondary pollution caused by leachate and the emission of methane, a potent greenhouse gas. Biosolids contain nutrients and energy that can be used beneficially. Significant efforts have been made recently to develop new technologies to manage biosolids and make useful products from them. In this paper, we provide a review of the technologies in biosolids management.Materials and methodsA survey of literature was conducted.ResultsAt present, the most common beneficial use of biosolids is agricultural land application because of inherent fertilizer values found in biosolids. Expansion of land application, however, may be limited in the future because of more stringent regulatory requirements and public concern about food chain contamination in some countries. Perceived as a green energy source, the combustion of biosolids has received renewed interest. Anaerobic digestion is generally a more effective method than incineration for energy recovery, and digested biosolids are suitable for further beneficial use through land application. Although conventional incineration systems for biosolid management generally consume more energy than they produce because of the high moisture content in the biosolids, it is expected that more combustion systems, either monocombustion or cocombustion, will be built to cope with the increasing quantity of biosolids.DiscussionUnder the increasingly popular low-carbon economy policy, biosolids may be recognized as a renewable fuel and be eligible for ‘carbon credits’. Because ash can be used to manufacture construction materials, combustion can provide a complete management for biosolids. A number of advanced thermal conversion technologies (e.g., supercritical water oxidation process and pyrolysis) are under development for biosolids management with a goal to generate useful products, such as higher quality fuels and recovery of phosphorus. With an ever-increasing demand for renewable energy, growing bioenergy crops and forests using biosolids as a fertilizer and soil amendment can not only contribute to the low-carbon economy but also maximize the nutrient and carbon value of the biosolids.ConclusionsLand application of biosolids achieves a complete reuse of its nutrients and organic carbon at a relatively low cost. Therefore, land application should become a preferred management option where there is available land, the quality of biosolids meet regulatory requirements, and it is socially acceptable. Intensive energy cropping and forest production using biosolids can help us meet the ever-increasing demand for renewable energy, which can eliminate the contamination potential for food sources, a common social concern about land application of biosolids. In recent years, increasing numbers of national and local governments have adopted more stringent regulations toward biosolid management. Under such a political climate, biosolids producers will have to develop multireuse strategies for biosolids to avoid being caught because a single route management practice might be under pressure at a short notice. Conventional incineration systems for biosolids management generally consume more energy than they produce and, although by-products may be used in manufacturing, this process cannot be regarded as a beneficial use of biosolids. However, biosolids are likely to become a source of renewable energy and produce ‘carbon credits’ under the increasingly popular, low-carbon economy policy.Recommendations and perspectivesTo manage biosolids in a sustainable manner, there is a need for further research in the following areas: achieving a higher degree of public understanding and acceptance for the beneficial use of biosolids, developing cost-efficient and effective thermal conversions for direct energy recovery from biosolids, advancing technology for phosphorus recovery, and selecting or breeding crops for efficient biofuel production.

Development of models to predict Pinus radiata productivity throughout New Zealand

Development of spatial surfaces describing variation in productivity across broad landscapes at a fine resolution would be of considerable use to forest managers as decision support tools to optimi...

Environmental and nutritional responses of a Pinus radiata plantation to biosolids application

Since the mid-1990s, a Pinus radiata (D. Don) plantation growing on a sandy, low fertility soil at Rabbit Island near Nelson, New Zealand received aerobically digested liquid biosolids. An experimental research trial was established on the site to investigate the effects of biosolids applications on tree growth, nutrition, soil and ground water quality. Biosolids were applied to the trial site in 1997 and 2000, at three application rates: 0 (control), 300 (standard) and 600 kg N ha−1 (high). Biosolids application significantly increased tree growth. This was mainly attributed to improved N supply, demonstrated by the enhanced N concentration in the tree foliage. Soil analysis indicated that biosolids application have not caused significant changes in concentrations of most nutrients. However, biosolids treatments significantly increased the available P (Olsen P). Of the heavy metals only total Cu concentrations in the soil increased after biosolids application. Groundwater quality, which was monitored quarterly, has not been affected by biosolids application. The concentrations of nitrate and heavy metals in groundwater were well below the maximum acceptable values in drinking water standards. Biological treatment of sewage and digestion of sewage sludge resulted in the enrichment of 15N in the biosolids (δ15N values between 5.0 and 8.7‰). Such enrichment was used as a tracer to study the fate of biosolids derived N. The elevated δ15N in biosolids treated pine foliage indicated that a considerable amount N was sourced from biosolids. Analysis of δ15N in understorey plants showed that both non-legume and legume understorey plants took up N from the biosolids, and acted as a N sink, reducing N availability for leaching. Our study showed that application of biosolids to a plantation forest can significantly improve tree nutrition and site productivity without resulting in any measurable adverse effect on the receiving environment.

Potential for the use of GIS and spatial analysis techniques as tools for monitoring changes in forest productivity and nutrition, a New Zealand example

A scheme for combining forest data (growth, foliar nutrition) and soil and site information in a predictive spatial system is proposed to address the following questions: Can geostatistics be used to produce maps of forest sustainability indicator variables such as tree growth or foliage and soil properties to show spatial and temporal trends? Can soil map units be used to stratify forests according to certain criteria and what are the implications of such a stratification on sampling needs? Is a GIS the logical tool for analysis and presentation of trends? We concluded that geostatistics is a valid tool for estimating and interpreting spatial trends in growth (site index) and foliar data (foliar P), but that in the study area available soil and foliage data was too sparse for confident use of this technique. Soil map units were used to stratify the study forest for growth, foliar P nutrition and soil P concentration, but at the selected map scale this only led to sampling efficiencies for the foliar N data. A modelled example of how the GIS and soil map units could be used to illustrate predicted changes in productivity and P status over space and time was presented. Soils were ranked according to their resilience to changes in P status based on initial soil P concentration, soil volume, and P fixing character. Likely changes in foliar P concentration in P. radiata stands on such sites were estimated over two rotations and changes in overall forest productivity predicted. In this study, based on existing available forest data, it became apparent that monitoring systems for site quality will not be able to depend on such data alone, and structured explicit sampling designs will be needed to address the requirements of long-term monitoring programmes. Tree-based indicators will be easier and cheaper to monitor than soil-based indicators, but a mix of both indicator types is likely in future schemes. # 1999 Elsevier Science B.V. All rights reserved.

Scaling up or scaling down: the use of foliage and soil information for optimising the phosphate nutrition of radiata pine

Fertilising with phosphate is important in New Zealand radiata pine plantations. Phosphate fertiliser trials have provided functions for determining potential growth gains from stands based on foliar P status. We used the national foliage database to determine the proportion of forest stands likely to be deficient in NZ. This gave a statistical representation but without a spatial reference. We used a nested design to test the spatial representation of foliar nutrient status and responsiveness at varied map scales. First we used the national soil map (1:10 6 scale) to show where P deficiency, and hence response, was most likely to occur. It was apparent that this representation was not acceptable for any operational scale planning. General trends in foliar status could be seen but there was no way of defining where foliage sampling should be concentrated within soil units, leading to inefficient sampling strategies. We then concentrated on the pumice, allophanic and podsol soil orders in the central North Island and used foliage data associated with 1:100,000 scale soil series map units. The spatial variation in likelihood of P deficiency and responsiveness was much clearer at this scale and more efficient foliar sampling programmes could be designed. At the most intensive scale (1:10,000) there were further gains to be made in foliage sampling efficiency and identification of responsive sites in some, but not all cases, and this depended on the soil pattern. We then tested whether spatial analysis of foliage data without reference to soil was better than using soil series as a defining class. Semivariograms constructed for foliar P concentration indicated that errors involved with predicting foliar P concentration were no less than if soil series was used as a predictor of foliar P status and responsiveness. We concluded that 1:100,000 soil series maps were adequate for general nutritional management planning and definition of areas likely to be responsive. However, for really precise work 1:10,000 maps would give additional definition for P fertilisation operations and allow us to refine fertiliser prescriptions at the within stand scale in some cases. # 2000 Elsevier Science B.V. All rights reserved.

Carbon and net nitrogen mineralisation in two forest soils amended with different concentrations of biuret

Abstract Biuret is a known contaminant of urea fertilisers that might be useful as a slow release N fertiliser for forestry. We studied carbon (C), net nitrogen (N) mineralisation and soil microbial biomass C and N dynamics in two forest soils (a sandy loam and a silt loam) during a 16-week long incubation following application of biuret (C 23.3%, N 40.8%, O 30.0% and H 4.9%) at concentrations of 0, 2, 10, 100 and 1000 mg kg−1 (oven-dried) soil to assess the potential of biuret as a slow-release N fertiliser. Lower concentrations of biuret specifically increased C mineralisation and soil microbial biomass C in the sandy loam soil, but not in the silt loam soil. A significant decrease of microbial biomass C was found in both soils at week 16 after biuret was applied at higher concentrations. C mineralisation declined with duration of incubation in both soils due to decreased C availability. Biuret at concentrations from 10 to 100 mg kg−1 soil had a significantly positive priming effect on soil organic N mineralisation in both soils. The causes for the priming effects were related to the stimulation of microbial growth and activity at an early stage of the incubation and/or the death of microbes at a later stage, which was biuret-concentration-dependent. The patterns in NH4+-N accumulation differed markedly between the two soils. Net N mineralisation and nitrification were much greater in the sandy loam soil than in the silt loam soil. However, the onset of net nitrification was earlier in the silt loam soil. Biuret might be a potential slow-release N source in the silt loam soil.

Differential Fertilisation of Pine Plantations on Acid Forest Soils

SYNOPSIS An approach to mapping plantation sites for fertilisation at different rates is discussed and compared with the generally accepted recommendations of 35 kg per hectare P. Fertilisation of sites in the Tsitsikamma Key Area with a rooting depth of 500 mm or greater resulted in a saving of potentially misapplied phosphate of 24%. Fertilising based on a regression model for increasing the soil Bray 2 levels to 12 mg/kg resulted in a further potential saving of 46%. based on a map of predicted rates computed from soil characteristics using a mean rate. of 18,9 kg/ha P: Variables studied showed spatial dependence and so we recommend the use of geostatistics in survey planning and mapping as this allows more efficient use to be made of spatial data. Results from this paper show promise for improving the forestry managers flexibility and aiding his decision-making.

Magnesium fertiliser dissolution rates in pumice soils under Pinus radiata

Application of Mg fertilisers has been suggested as a means of reducing the incidence of Mg deficiency of forest trees in New Zealand and Europe. The objective of this study was to determine the rates of dissolution of a range of Mg fertilisers applied to a pumice soil (Typic Udivitrand). The rate of fertiliser dissolution was little influenced by whether the fertiliser was applied directly on to the soil surface (litter removed) or on to the litter layer in a Pinus radiata plantation. Twenty-seven months since fertiliser application the mean (with and without litter) percentage of Mg dissolved was in the sequence: Epsom salts > calcined magnesite 1–2 mm > granmag (a partially acidulated and granulated calmag product) > calcined magnesite 2–4 mm > forestry grade dolomite. The specific dissolution rate constants (mg/cm2 .day of fertiliser) for the slowly soluble Mg fertilisers calculated using an elemental sulfur oxidation cubic model were 587 for calcined magnesite 1–2 mm, 426 for calcined magnesite 2–4 mm, 385 for granmag, and 18 for forestry grade dolomite. In a laboratory incubation study the elemental sulfur oxidation cubic model described the rate of dissolution of Mg fertilisers within narrow fertiliser particle size ranges. The specific fertiliser dissolution rate constants, however, increased with decreases in particle size, suggesting that the rate of dissolution depends on factors other than surface area when particle sizes varied widely. Slowly soluble, alkaline Mg fertilisers had a significant liming effect on the soil. They were more effective in increasing soil exchangeable Mg than soluble Mg salts over a long-period and therefore, they are better fertilisers for P. radiata.

Factors Affecting Soil Phosphate Distribution and Reactions in Cape Forest Soils

SYNOPSIS The amounts of various forms of phosphate in some Cape soils and the adsorption of phosphate by these soils were investigated. The levels were low and only 2% was in available form. The major fraction of phosphate in the soil was organic phosphate. Aluminium phosphate and iron phosphate were the next largest fractions. Aluminium phosphate concentrations were related to soil organic carbon, and iron phosphate concentrations to clay and silt content. Adsorption of phosphate was low to moderate and was correlated to organic carbon, pH in sodium fluoride and fine silt content. In these soils, exchange sites associated with the fine silt fraction seem to be more important to phosphate adsorption than those associated with the clay fraction. The amount of phosphate fertiliser calculated from buffering capacity was lower than the current recommended rate for most of the soils tested. From these studies fixation of phosphate does not appear to be a major problem in plantation soils in the Cape regions; l...

A sequential extraction method for the determination of dissolution of magnesium from fertilizers applied to pumice soils

Abstract A major factor controlling the effectiveness of magnesium (Mg) fertilizers in correcting Mg deficiency in crops is their rate of dissolution in soils. The commonly used method of determining the rate of dissolution of fertilizers by measuring the increase in dissolved Mg in soils under field conditions can lead to errors because part of the dissolved Mg would normally be lost from the site of application by plant uptake and leaching. A more accurate method of estimating the rate of dissolution is to determine the amount of undissolved Mg and subtract it from the amount of Mg applied. A simple sequential extraction method was developed to measure the undissolved Mg in soils treated with a range of fertilizers with different solubilities. The method consisted of two 30‐minute extractions of a soil sample with 0.5M BaCl2‐TEA, pH 8.2 to determine dissolved Mg in the sample followed by a 1‐hour extraction with 0.5M HCl to determine difficulty‐soluble or slow‐release Mg, and finally an 18‐hour extracti...