Infiltration Lagoons as a Tertiary Treatment Device

As the United States continues to grow and expand industrially, increased mechanization and shorter work weeks will result in a populace which will expect to enjoy increasing amounts of leisure time. Part of this leisure time will be used to participate in outdoor recreation activities, the result being an increased demand on lakes and streams. Maintaining these waters in a suitable condition for recreation and other beneficial uses has become the concern of most Americans. The Water Quality Act of 1965 and the subsequent state water quality standards are ample proof of the concern given to the control of water pollution. In direct conflict with many beneficial uses is the discharge of sewage effluents into lakes and streams. Present biological sewage treatment plants are capable of producing highly stabilized effluents in terms of oxygen depleting materials, but most are incapable of reducing concentrations of phosphorus or nitrogen by an appreciable amount. In recent years the problem has been compounded because of a dramatic increase in the use of synthetic detergents (l-1259). The discharge of phosphorus and nitrogen into waterways is of concern because they act as fertilizers and stimulate the growth of aquatic weeds and algae. Lakes are particularly vulnerable because they act as nutrient traps, storing phosphorus and nitrogen in their bottom sediments. In shallow lakes these nutrients are readily released for plant utilization by wave action or any other bottom disturbance. Nutrient-rich or eutrophic lakes inevitably result in reduced aesthetic and property values, thus limiting their capacity to satisfy the needs of other beneficial uses. Troublesome growths of aquatic weeds and algae interfere with boating, fishing, and swimming activities; and they also create problems in water treatment plants by imparting tastes and odors to waters. Most small communities have not yet seen a need for the removal of nutrients from their sewage discharges. However, many people are becoming concerned with the increased incidence of fish kills and troublesome algal blooms in their favorite lakes. Although nutrient influx from the discharge of sewage is not the only contributor to eutrophic conditions, it is an important factor which must be controlled if the life of a lake is to be extended. Present phosphate removal processes are based primarily on precipitation with lime, and consequently the reduction of phosphate to acceptable levels is a very expensive process. A lime-biological treatment scheme reported by Schmid and McKinney appears to be more economical than precipitation processes alone, but this concept is adaptable only to activated sludge treatment plants. Many South Dakota communities would encounter problems when confronted with the need to remove nutrients because many utilize stabilization ponds as their only treatment facility, and these would be very difficult to adapt to precipitation processes. Other communities employ trickling filter plants which would need to rely entirely on chemical precipitation to remove the phosphorus and nitrogen; this process would require both trained operators and large quantities of chemicals. One of the most promising methods that the small community can economically use in reducing phosphorus and nitrogen in their treatment plant effluents is to apply these effluents to the land. This method may be accomplished with irrigation or by discharge to seepage beds or infiltration lagoons. These systems all work on the principle that, during the infiltration and percolation processes that occur, the phosphorus and nitrogen concentrations are reduced through filtration and adsorption to the soil particles. The specific objective of this study was to evaluate the infiltration lagoon concept as a wastewater treatment device by comparing the quality of lagooned wastewater to the quality of lagoon seepage. This objective was accomplished by determining the effectiveness of several infiltration systems that are currently functioning. These systems were not purposely designed for this function; rather they were constructed as lagoons, but because of their extraordinarily high seepage rates, they now serve in the capacity of infiltration lagoons. The parameters used in this evaluation included chloride, phosphate, kjeldahl nitrogen, nitrate, chemical oxygen demand, bacteria, and specific conductance

Optimization of Pavement Marking Performance

Pavement markings must perform on a variety of asphalt and concrete surfaces. Surface preparation can also affect a markings initial visibility and long-term performance. Therefore, there is a need for information on the performance of pavement markings under many conditions including type of pavement, type of marking, etc. but particularly the degree and type of winter maintenance. This need is satisfied by the research presented in this paper on pavement marking materials that assess durability and visibility, and in improved procedures of marking material evaluation and selection. A field testing program was initiated to evaluate the durability and visibility of alternative pavement marking materials and application practices of various paints, in consideration of the South Dakota Department of Transportation’s pavement construction and maintenance practices. Six field test sections were constructed at various locations in South Dakota to assess the performance of 69 combinations of paint type, paint thickness, line type, reflective element type, pavement type, pavement preparation method, and winter maintenance region. The markings were evaluating using retroreflectivity and visual rating. From the collected data, degradation models were created using exponential models presented in the literature. The degradation models were implemented by using practical methods for assessing pavement marking retroreflectivity and costs. The methods presented in this paper include parametric analyses and a cost comparison method. These methods can be used in assessing life expectancy as well assessing costs for evaluating marking alternatives