Effects of pre-treatment technologies on quantity and quality of source-sorted municipal organic waste for biogas recovery

Source-sorted municipal organic waste collected from different dwelling types in five Danish cities and pre-treated at three different plants was sampled and characterized several times during one year to investigate the origin of any differences in composition of the pre-treated waste introduced by city, pre-treatment technology, dwelling type or annual season. The investigated pre-treatment technologies were screw press, disc screen and shredder+magnet. The average quantity of pre-treated organic waste (biomass) produced from the incoming waste varied between the investigated pre-treatment technologies: 59%, 66% and 98% wet weight, respectively (41%, 34% and 2% reject, respectively). The pre-treatment technologies showed differences with respect to distribution of the chemical components in the waste between the biomass and the rejected material (reject), especially for dry matter, ash, collection bag material (plastic or paper) and easily degradable organic matter. Furthermore, the particle size of the biomass was related to the pre-treatment technology. The content of plastic in the biomass depended both on the actual collection bag material used in the system and the pre-treatment technology. The sampled reject consisted mostly of organic matter. For cities using plastic bags for the source-separated organic waste, the expected content of plastic in the reject was up to 10% wet weight (in some cases up to 20%). Batch tests for methane potential of the biomass samples showed only minor variations caused by the factors city, pre-treatment technology, dwelling type and season when based on the VS content of the waste (overall average 459STPm(3)/tVS). The amount of methane generated from 1t of collected waste was therefore mainly determined by the efficiency of the chosen pre-treatment technology described by the mass distribution of the incoming waste between biomass and reject.     

Sterol production and phytosterol bioconversion in two species of heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans

The kinetics and efficiency of sterol production and bioconversion of phytosterols in two heterotrophic protists Oxyrrhis marina and Gyrodinium dominans were examined by feeding them two different algal species (Rhodomonas salina and Dunaliella tertiolecta) differing in sterol profiles. R. salina contains predominantly brassicasterol (≅99%) and <2% cholesterol. The major sterols in D. tertiolecta are ergosterol (45–49%), 7-dehydroporiferasterol (29–31%) and fungisterol (21–26%). O. marina fed R. salina metabolized dietary brassicasterol to produce 22-dehydrocholesterol and cholesterol. O. marina fed D. tertiolecta metabolized dietary sterols to produce cholesterol, 22-dehydrocholesterol, brassicasterol and stigmasterol. G. dominans fed either R. salina or D. tertiolecta metabolized dietary sterols to make cholesterol, brassicasterol and a series of unknown sterols. When protists were fed R. salina, which contains cholesterol, the levels of cholesterol were increased to a magnitude of nearly 5- to 30-fold at the phytoplankton-heterotrophic protist interface, equivalent to a production of 172.5 ± 16.2 and 987.7 ± 377.7 ng cholesterol per mg R. salina carbon consumed by O. marina and G. dominans, respectively. When protists were fed D. tertiolecta, which contains no cholesterol, a net production of cholesterol by the protists ranged from 123.2 ± 30.6 to 871.8 ± 130.8 ng per mg algal C consumed. Cholesterol is not only the dominant sterol, but a critical precursor for many physiologically functional biochemicals in higher animal. As intermediates, these heterotrophic protists increase the amount of cholesterol at the phytoplankton–zooplankton interface available to higher trophic levels relative to zooplankton feeding on algae directly.     

EFFECTS OF INCREASED DELTA EXPORTS ON SACRAMENTO VALLEY'S ECONOMY AND WATER MANAGEMENT1

ABSTRACT: Exports from the Sacramento‐San Joaquin Delta are an important source of water for Central Valley and Southern California users. The purpose of this paper is to estimate and analyze the effects increased exports to south of Delta users would have on the Sacramento Valley economy and water management if water were managed and reallocated for purely economic benefits, as if there were an ideal Sacramento Valley water market. Current Delta exports of 6,190 thousand acre‐feet per year were increased incrementally to maximum export pumping plant capacities. Initial increases in Delta exports did not increase regional water scarcity, but decreased surplus Delta flows. Further export increases raised agricultural scarcity. Urban users suffer increased scarcity only for exports exceeding 10,393 taf/yr. Expanding exports raises the economic value of expanding key facilities (such as Engle bright Lake and South Folsom Canal) and the opportunity costs of environmental requirements. The study illustrates the physical and economic capacity of the Sacramento Valley to further increase exports of water to drier parts of the state, even within significant environmental flow restrictions. More generally, the results illustrate the physical capacity for greater economic benefits and flexibility in water management within environmental constraints, given institutional capability to reoperate or reallocate water resources, as implied by water markets.     

The fatality consequences of the 65 mph speed limits, 1989

This study examined whether the number of fatalities on rural interstates in 1989 was higher than would be expected based on experience during 1982–1986 and experience on all other roads. Among the 40 states that increased the speed limit to 65 mph on rural interstates, the number of fatalities was 29% higher than expected. Among the eight states retaining a 55 mph maximum speed limit on rural interstates, the observed number of fatalities was 12% lower than expected, although this reduction was not statistically significant. After adjusting the fatality risk on rural interstates for differences in vehicle miles traveled on those roads and for higher passenger vehicle occupancy rates attributable to possible increases in vacation travel, the increased fatality risk was 19%. These data suggest that the majority of the estimated increase in fatalities on rural interstates in 1989 (almost 400 of the approximately 600 extra deaths) can be attributed to the higher speeds resulting from the higher speed limits. Changes in mileage account for the remaining 200 extra deaths.     

Redistribution of slurry components as influenced by injection method, soil, and slurry properties

The distribution of moisture, degradable C, and N after direct injection of slurry can affect the turnover and plant availability of slurry N. This study examined effects of injection method, soil conditions, and slurry properties on the infiltration of several slurry components under practical conditions. The water retention capacity of 22 pig and cattle slurries was quantified by dialysis at -0.016, -0.047, and -0.100 MPa. All slurries followed the relationship: relative water loss = 1/(1 + aVS[volatile solids]), indicating that retention of liquids in the slurry injection zone can be predicted from slurry VS and soil water potential. Two-disc injection and harrow tine injection were simulated (no slurry applied) in five trials. Two trials indicated that disc injection resulted in higher permeability compared with harrow tine injection. In a separate experiment, soil moisture and dissolved ions were monitored in and around injection slits amended with pig or cattle slurry. Moisture gradients, which were recorded with small printed-circuit-board (PCB) time-domain-reflectometry (TDR) probes, were temporally stable and reestablished following rainfall. Slit sections with pig and cattle slurry containing 13C-acetate and 15N-ammonium showed a shift in the 13C to 15N ratio of the injection zone within 24 h, which was explained by removal of dissolved C and/or retention of NH4+. Cattle slurry was more concentrated around the injection slit than pig slurry, and greater contact between slurry and soil was obtained with harrow tine injection. The heterogeneity of slurry C and N distribution after direct injection should be accounted for in models describing slurry N turnover.     

The environment and Britain's aid programme

Summary Some of the environmental and developmental activities assisted by Britain's Programme of Overseas Aid are outlined. In particular, the article draws attention to a new booklet published by the Overseas Development Administration to mark the European Year of the Environment which, in the Minister's words, shows how through British aid, programme improvements are possible by a combination of sound scientific research and a sensitivity to people's needs.Mr Christopher Patten, Member of Parliament for Bath, is the UK's current Minister for Overseas Development. He also serves as Minister of State for Foreign and Commonwealth Affairs. The Minister may be contacted through the offices of the Overseas Development Administration, Eland House, Stag Place, London SW1E 5DH, UK.     

Outlining a Conception of Animal Welfare for Organic Farming Systems

The concept of animal welfare refersto the animal's quality of life. The choice ofdefinition always reflects some basicvaluation. This makes a particular conceptionof welfare value-dependent. Also, the animalhusbandry system reflects certain values oraims. The values reflected in the chosenconception of animal welfare ought tocorrespond to values aimed for in the husbandrysystem. The IFOAM Basic Standards and otherwritings dealing with organic animal husbandryshould be taken as a departure point for adiscussion of how to interpret the conceptionof welfare in organic farming systems. Theconception of welfare is related to two corevalues in the organic agriculture movement.These core values should be considered in termsof (1) aim for holistic view and (2) aim forsustainability. A third, implicit core value,based on bio- and ecocentric views: (3) respectfor nature is needed as a supplement to thesetwo core values. There are importantimplications of these core values for an``organic' conception of animal welfare and forconfronting two dilemmas due to conflictinginterests. Comparisons among the three commonlyused welfare definitions will show thesuperiority of the third approach, which canprovide an outline for a conception of animalwelfare more suitable for organic farmingsystems. This outline combines a holisticecocentric approach with respect for theindividual animal, and it can be used as thebasis for a complex definition with emphasis onnatural behavior. Such a systemic approachconsiders welfare in relation to differentsystemic levels. The systemic view also offerspossibilities for resolving the dilemmas in newways.