The Use of Biosolids and Other Organic Substances in the Creation of Soil-Forming Materials

This paper describes an experiment which was carried out at a landfill site in north Lincolnshire to investigate the use of biosolids and other organic materials in soil formation. The following organic amendments were incorporated into the surface of the on-site geological clay to form 'topsoil'treatments: (i) nil, (ii) biosolids (digested cake), (iii) waste peat/compost, and (iv) composted green waste. The biosolids were applied at a rate of 70 tDS/ha and all the organic materials were incorporated to a depth of 150 mm. The organic amendments reduced the topsoil bulk density and increased plant available water supply and soil water infiltration rates. Topsoil organic matter, total nitrogen and extractable phosphorus concentrations, biomass nitrogen, readily mineralisable organic nitrogen and soil respiration rates were also increased. Additionally, the biosolids application increased topsoil aggregate stability and soil surface strength.     

MODELLING THE IMPACT OF CLIMATE CHANGE ON DOMESTIC WATER DEMAND

This report paper examines current domestic water demand elasticity, with weather variables, as an aid to assessing the potential impact of climate change on domestic water demand. An empirical model of the relationship between summer domestic water demand and concurrent weather under current climatic and socio-economic conditions is developed and then applied to weather data which have been produced for 2020AD climate scenarios. The model is based on data for the Essex area supplied by Essex and Suffolk Water. The results suggest an increase in summer seven-day average domestic-water demand of 3.3 l/hd. d (range 1.37–5.72 l/hd. d), in addition to an increase in the frequency of large demand events. The analysis forms the basis of a wider exposition, examining future domestic water demand under varying climate-change scenarios.     

Agricultural Utilization of Sewage Sludge: A Review

Utilization on agricultural land is the principal outlet for sewage sludge in the UK, accounting for about 40% of the annual production. During the last 30 years current practice has developed to maximize the benefits to farmers whilst controlling potential problems of public nuisance, water pollution, pathogen transmission and soil contamination. Until now this has been achieved by Government guidelines but, in future, utilization of sewage sludge in agriculture will have a statutory basis following the implemention of an EC Directive in June 1989.
A copy of the discussion to this paper, and a copy of the full version of the proceedings of the Symposium, can be obtained from the Institution's Headquarters.     

Preliminary Results of the Anaerobic Biotreatability of the Effluent from the Wet-Air Oxidation of Sewage Sludge

Wet air oxidation and other thermal processes can be used on all sludges, whether they are raw, mixed or digested. The process sterilizes the sludge and gives a considerable reduction in volume. However, apart from the high capital costs which are associated with this technique, one of its principal disadvantages is the high strength of the (effluent) liquor.
This study investigated the feasibility of treating the liquor using an anaerobic digester, which resulted in a good reduction in BOD and a reasonable reduction in COD. The liquor was still strong, but could be returned to the inlet works of a sewage-treatment plant without causing significant organic overloading.     

Phosphorus Release and Fertiliser Value of Enhanced-Treated and Nutrient-Removal Biosolids

This paper describes a soil-incubation study which was carried out to examine the effects of (a) phosphorus removal during the treatment of domestic sewage and (b) treating sewage sludge to an enhanced status, on the phosphorus fertiliser value of biosolids which are used in agriculture. Phosphorus-enriched and conventional dewatered digested biosolids, thermally-dried pellets and granules, and digested and thermally-hydrolysed liquid sludges were incorporated into two soil types with contrasting physico-chemical properties. Plant-available phosphorus in soil was assessed after incubation by a standard chemical-extraction procedure. Sludge from biological-P removal had the highest phosphorus extract-ability in soil whereas iron dosing slightly reduced or had no effect on phosphorus release from conventionally-treated biosolids, depending upon the type of soil. High-temperature drying significantly reduced the extractable-P content in sludge by 20–60%, compared with dewatered digested cake, and release from thermally-dried biosolids declined further with iron enrichment. Extractable-P recovery was greater from all types of biosolids when mixed with calcareous soil, compared with a loamy sand. A preliminary investigation of phosphorus mineralogy in biosolids, using advanced analytical techniques, is also described.     

Peak Demands from Spray Irrigation

Although irrigation accounts for less than 2% of water use in the UK, direct abstraction for spray irrigation can be a significant user in certain catchments in dry summers. Peak demand is expected to grow nationally by 1–2% per annum on average, but this growth varies locally. Water resource planners need to know the peak demands and how they are likely to grow within each catchment or aquifer, and the likely local annual variation and timing of demand. This paper discusses how recent developments in irrigation modelling combined with the application of a 'geographic information system'can produce such forecasts, taking into account spatial variation in soils, climate, cropping and irrigation practice.     

The Use of Bone Charcoal in the Treatment of Rural Water Supplies

As a result of the Water Act of 1989 on the quality of water intended for human consumption, a number of small spring sources in Yorkshire were the subject of legal undertakings for remedial action to reduce the concentration of trihalomethanes in the distribution system. The trihalomethanes are formed when the colour in these waters, which is made up of predominantly fulvic and humic acids, is chlorinated. Therefore, in order to solve the problem of trihalomethanes in treated water, colour removal was necessary.
The paper describes the use of bone charcoal in slow sand filters to remove colour from rural water supplies. It covers six months pilot-plant work which was undertaken at Marsett water-treatment works (near Richmond), and the implementation at other plants within Yorkshire. low-rate filtration through bone charcoal ensured that the colour and trihalomethane concentrations in filtered water complied with EC standards, and the material coped well with rapid changes in raw water quality.     

Hazardous Waste: Future Consideration

In most industries the goods and money move in opposite directions, but in waste management the goods and money travel in the same direction. Consequently to the customer, quality of goods and service might be measured only by price. However, customers are now becoming more sensitive to factors such as environmental quality. They are also becoming aware of the range of disposal options, together with the names of the companies which operate these disposal or treatment sites. Essentially the options are: recyling and recovery, sea disposal, landfill, physico-chemical treatment, solidification, biological treatment and thermal destruction. The Control of Pollution Act 1974 requires that all landfill sites and treatment centres are licensed by the waste disposal authority. These authorities are obliged to act in the public interest, and hence there is a complex interaction of science and politics. This situation often gives rise to localized opposition to facilities which are needed by the community. The UK disposes of 83 per cent of its potentially difficult wastes to landfill whilst Holland disposes of 52 per cent via this route. The cost of disposal varies throughout Europe but, in general, prices in the UK are lower than in Europe, which has led to the importation of wastes from the continent. Economics applies to the waste-disposal industry as much as any other industry, therefore facilities are supplied in response to demand. Price alone will not always be adequate in obtaining the ‘best practical environmental option’. disposal the goods and the money go in the same direction, i.e. to the waste management contractor. This at first sight may not seem important until it is realized that the major control upon the quality of a service is, in fact, the satisfaction with the goods and service which the customer receives. In most cases it is sufficient that the customer disposes of the waste material in a legal manner. However, the judgement of quality of disposal could be of little consequence to him. The factors that concern a customer when he chooses a service include the price, the quality of service, market presentation and reputation. These factors apply in the waste management industry, but the difficulty for the customer is to judge the quality of the service and the market presentation or, more correctly in this case, the quality of operation of the waste contractor. If the latter two factors become difficult to judge, the price becomes a critical factor. This leads to a low standard of operation in the business where price competition becomes more important than the quality of the service. Companies are looking not just for the cheapest legal option but for the best option and what has been referred to as the ‘best practical environmental option’. In the UK the vast majority of hazardous waste disposal is carried out by private-sector companies. Therefore it is essential that the Government sets the correct framework, and that an examination is carried out as to whether the framework is satisfactory and whether it achieves the needs of the Government.     

Process Options for Phosphorus and Nitrogen Removal from Wastewater

The paper reviews the current capabilities of processes for phosphorus and nitrogen removal in relation to the EC urban waste water treatment Directive. The Directive is briefly described and the implications for the UK are discussed. This is followed by a review of biological and chemical processes for nutrient removal with special reference to their current state of application and performance. Particular attention is paid to processes for biological phosphorus removal which, in the past, was said to be less reliable than the chemical options but which is now being more widely applied in other parts of Europe as well as South Africa and North America. Processes for modifying both activated sludge and biological filter systems to meet the Directive are briefly described.